My sister said she didn't like how in D&D you can die, and suggested checkpoints, what would be the best way to do that, should I have them save whenever they want, or just after major bosses?
What's wrong with dying?
I guess the first question is, what's the big deal with dying? Dying in Dungeons and Dragons is just the "losing" condition of other games. Card games have non-winners. Board games have non-winners. And the first generations of video games existence have a "Game Over" situation by running out of lives, running out of time, unable to collect resources, etc with no way to start from the point of final death. When you run out of room for Tetris pieces, you don't go back to a "save point" and try again. It's just done and you start from the beginning.
Dying/losing is part of playing a game.
It's harder than you think
Dungeons and Dragons (focusing on 5e), actually makes it really hard to completely "die".
All characters have hit points (hp) which is a value to determine how hardy a character is. When a character takes damage, that value is decremented, but there are many way to bring that value back up to a character's maximum. In fact, with temporary hit points, a character can even go higher than their maximum.
Characters are still alive, awake, and at full power so long as that value is 1 or higher. So whether they have 100 hp or 1 hp, the character is fine and not limited in any way 1.
If something does manage to bring the character to 0, they are merely unconscious, not dead. The exception being is if the character takes massive damage from a single blow that would reduce their hp to a negative value more than or equal to their maximum hp (so if the character has a max 12 hp, something, in one blow, causes them to go to -12 or lower), but that is extremely rare. There are a few spells and effects that can outright kill someone. But those are rare as well and even then, the wish spell usually can bring a character back.
Now that the character is unconscious, they start Death Saving Throws. Basically a best 3 out of 5 in rolling 10 or higher on a d20 (so a better than 50/50 chance on each roll). That's still at least two or three rounds of only being unconscious, not dead. Also, any of your teammates can take actions to bring the character back to consciousness (or at least stabilized):
- Spare the Dying spell to stabilize the character
- Cure Wounds spell
- Healing Word spell
- Heal spell
- Potions of Healing
- Medicine check to stabilize the character
- Healing kits to stabilize the character
- Character class features
- and many, many more...
Any of these will, at minimum, stop your character from dying. But any healing spell pops the character back up, ready for more.
Now, say none of that happens... Then your character is only "mostly dead".
Even after death, there are spells than can bring a character back to life like revivify, resurrection, reincarnation, and wish. All with different limits, availability, and successes.
On top of all that, there is a clone spell so that if a character dies, their soul is instantly transported to the clone vessel and can start afresh.
So the act of dying is NOT an every day occurrence for the average adventurer.
The party may not have access to all of these spells at the time of the death, but the world is full of NPCs that would be able to cast them for coin or other trade.
So you really want a save point?
Don't. Plain and simple, don't.
Why? Because unlike the video games your sister is likely patterning this against, D&D is a multi-player game. What happens if your character dies, but no one else does? Does your character mystically get transported back to a safe zone? Now everyone else has to journey back to to the safe zone meet up with your body (and bring you your clothes/equipment depending on how you design the save point). This will put a huge drag on the game.
Fighting "boss monsters" is not a common situation either (usually, although it depends on how the DM runs the game). So your character could go MONTHS without a "boss monster" save point. What happens to all the experience that happened between then and now? Items and knowledge gained? How do you ret-con all that time and adventuring?
So you really, really want a save point?
Don't call them save points. They are just beats in the story where a DM can bring anyone/everyone back due to an outside benefactor.
Whole party died? A necromancer brings them all back to do a "favor". One person died? Carry the dead to a nearby town where they can perform a resurrection for trade. Or maybe all the damage was subdual damage (non-lethal) and the attackers brought the party back to their lair for slavery or money.
Make death part of moving the story forward, not a reason to rewind.
1 There are other factors that can limit a character such as exhaustion, various conditions, spell effect, etc. But hit points are not a factor in limiting someone.
Actually dying in D&D is very rare (in most games)
In (most games of) D&D, the expectation is that the DM won't give you any challenge that's so hard that your character dies. If your character dies anyway, it's probably because the DM screwed up.
Some DMs like to run a more difficult game where encounters are very deadly and character death is common, but you can just choose not to do that.
You can choose the rewind point when it happens
This isn't a computer game. When (if) the characters die, you can decide to rewind time, and at that point you can decide how far back to rewind. I've done this on a few occasions, and I recommend rewinding as little as possible -- eg, to the first point where the group could make a decision that would stop them from dying.
Replaying parts of a D&D campaign might not be fun
D&D takes longer than most video games, and a lot of the fun comes from the novelty and exploration. Playing through a part of the adventure that you just played through might not be fun.
Even if you allow this in the case of accidental party deaths, I recommend not making "save points" a part of the fiction, so as to keep "replaying" very rare.
I don't think checkpoints are a good idea, per-se.
I think you should be willing to undo anything at any time, but try to avoid needing to do so.
Be willing to undo anything
Tabletop games are not meant to be challenging or frustrating. If events in game cause one of your players to be upset to the point that the game is no longer fun for them, you should be willing to undo that event, regardless of what that event was.
This goes even further than checkpoints or saving and loading. You should be willing to undo an encounter even if the players forgot to "save." If your players are frustrated and not enjoying the game, you must either be willing to fix the game by any means necessary, or be willing to cut those players loose.
This is called (one kind of) "script change," and is one of the many tools a GM has for keeping their players in the game.
Don't make undoing things part of the game
Unlimited access to script changes technically means that one player could decide that they don't have fun unless everything goes their way and ask you to script change every time they roll badly.
To protect against this, make it clear that tools like this should not be considered part of the game (mechanics that players are allowed to optimize), but rather part of the agreement to play the game. If a player doesn't agree to play the game unless their dice always roll winning numbers, then you might decide that maybe you don't want to play with that player after all.
At my tables: Whenever a player asks for something that could be considered a script change, I ask: "Are you asking for a script change, here?" If they say yes, I agree to implement the script change immediately, and ask one follow-up question, "Do you want to discuss this more later?" Regardless of their answer to the second question, play continues. If they do ask to talk about it later, I bring it up after the session with a focus on how I can give them the game they want so that they don't have to ask for a script change next time. If they don't want to talk about it later, I don't bring it up again and just continue with the new script.
I explain all of this (including the two questions I will ask) to my players before the first session.
I have never had a player abuse this option to cheat. (I've also never had a player answer "no" to the second question, though)
Try to avoid needing to undo things in the first place
Talk to your players ahead of time and find out what kind of game they want to play and (importantly), what kind of game they don't want to play, but that your system could theoretically push them into. I've got a couple points for how to do this.
If your players don't like dying, change the dying rules
If your players don't want to die and lose their PC, you can reassure them that it's very hard to actually die (as other answers have brought up) or even change the rules for dying so it doesn't happen. An effective house-rule I've seen for this is that death saves are rolled secretly by the dying player, and they are allowed to cheat on those rolls specifically.
If your players don't like being tricked, don't trick them
Consider the possibility that the story goes in a direction that the players don't want it to and they want to go back in time and make a choice differently now that they have more information. If this happens, that means that you tricked them (even if unintentionally) into taking the plot in an unpleasant direction.
Some players are fine with this. I'm such a player - anticipating the consequences of my actions and thinking my decisions through carefully is part of what I enjoy about RPGs. Other players are not okay with this, and will want a script change when it happens. As a GM, you should find out what kind of players you have. The easiest way is to ask them. (Players aren't always right about what they want, so even if they say they want to be tricked sometimes, you should be willing to stop tricking them if it doesn't work out.)
If your players don't want to be tricked, then avoid hiding things in your story. Have NPCs that are transparent about their plans and motivations, and if you think your players are about to make a bad decision, explain what the consequences of that decision could be and then ask if they really want to do that. This effectively gives them a chance to script change their decision before it becomes canonical, which is must less jarring than fixing it later.
Why not save points?
Save points are a thing computer RPGs created due to the constraints of their medium. One of the reasons why computer RPGs have checkpoints (besides the finality of death) is that a CRPG can only really tell a finite number of stories, which all must be written in advance. If anything happens that the designers of the CRPG didn't plan on happening (or didn't want to spend time and money developing a story branch for), the CRPG can only two do things: it can ignore it, or it can force the player to reset from an earlier point before things went off-script.
Experiencing the same story multiple times is usually less interesting than writing new stories
When players reload a game from a save point, they almost always end up skipping dialog/cutscenes that they've already seen before. Why wouldn't they? It's not new story - it's just busy work to get back to the part of the story they want to see. By-and-large, players prefer new stories unless those stories are upsetting.
In a tabletop game, you have the option to just fix the one thing that the players would want to go back and fix, without making them re-watch all the metaphorical cutscenes. I can't think of a good reason not to do that.
Undoing things in bulk (like a save point) is hard
Unlike a video game, which can persist the state of every NPC and every item, tabletop games exist only in the minds of the players (including the GM) plus whatever they're able to write down. Things like this work best if they only ever move forward - that is, if everything that the players can remember happening remains canonical.
Script changes work best if you excise the parts of the script that are upsetting people: "Okay, that encounter happened two weeks ago happened almost exactly as we remember it, but Shannon didn't die, she actually just got knocked out and has been in a coma ever since. She's all better now."
If you try to go back and undo a session (or worse, multiple sessions), it's easy as a GM to lose track of the story - unless you kept meticulous notes of the undone sessions, you might not remember which NPCs the PCs have met before versus are now meeting for the first time, or even which NPCs are still alive.
An unexpected TPK (Total Party Kill) can be a very anticlimatic ending to an RPG game. When everyone at the table agrees that they don't want the game to end like this, and rules be damned, you want to try again, then there is no RPG police that will burst into the room and stop you from doing that just because the rulebook doesn't have a chapter on that.
But you don't need explicit checkpoints as a homebrewed game mechanic for that to be possible. You can just negotiate at the table which point of the story was the "fatal mistake" that lead to the abrupt campaign ending, and rewind time to just before that. Sometimes while also making a couple changes to the world. For example, because the DM agrees that they screwed up and accidentally designed an encounter the party had no way to overcome. Or perhaps there was some communication failure when the DM described the situation that misled the players to do something stupid that seemed perfectly reasonable from how they understood the DMs narration. We have done that during various RPG sessions and it always worked out just fine.
Checkpoints in video games are a crutch for this, because the game can't have that negotiation with you. The game designers can only guess to which point you probably want to return after you die, which is why they place a checkpoint there. But as a human DM you are not bound to that limitation. You can do what a human DM does and improvise the best solution for the game on the spot.
Try to figure out why your players are scared of dying
Do they think they are bad at playing the game? Offer advice, suggest potential actions, and/or lower the difficulty of encounters.
Do they feel like dying is too sudden or unexpected? Maybe this is because of a communication breakdown. You could be more explicit about NPC motivations or how dangerous an encounter is.
Do they feel like they are "playing scared" and are not enjoying the game? Discuss how death can be meaningful. Or offer a some number of "extra lives" to help them deal with existential dread so they can play the game without that anxiety.
"Autosaves" when using a published module can make sense
Playing through a published adventure module can change players' expectations. Modules that were crafted by professional writers and game designers can make the adventure feel more like a videogame RPG. For example, players know there is at least one defined ending (especially a "good" ending).
PC death (and TPKs especially) can now feel unsatisfying if the players have a sense that they "died before they were supposed to." Players can tell they haven't made it to the final conflict/encounter. A TPK before then can feeling like reading half a novel before losing the book and never getting to finish it.
If the party all die (a TPK), it is often obvious that you could rewind to a point before the lethal encounter. Or you could start at an important plot point, which should be easy to identify with the source materials.
If only some of the party dies, you have a more difficult decision. Ideally, that's something you and your players have discussed ahead of time. Maybe your players are fine with creating a new character. Or maybe they want a new side quest to revive their fallen comrades. Or maybe they are perfectionists who really do enjoy trying to "solve" the puzzle of the encounter without anyone dying, and "reloading the autosave" is the solution. Regardless, you should just talk with your players about their expectations.
Just remove death
Characters don't have to die when they reach 0hp and fail their saves. Have them instead be unconscious and wake up hours later. A fallen PC can be recovered by the friends, taken hostage, or simply left for dead on the field of battle.
Or improve raising the dead
Make recovering dead characters easier. Give the spell at lower level to more classes and remove the cost and limitations. Maybe dead characters can simply be respawned using a spell when the PCs are back on safe ground, or maybe they need to leave a lock of hair somewhere safe so they can be reserrected from it.
Consider whether this is actually going to improve the game. Character death is rarely fun, but for most players the risk of death makes a positive contribution to the fun of the game. Without consequences for failure, you may well find the game loses a lot of tension and coherence.
Rather than repost, I will simply point to my answer here:
The short version, is that I have in past games attributed respawning to the gods, and respawn points are locations of importance to those gods.
Other answers say why checkpointing and coming back to life is a bad idea and ruins the fun of the game.
On the other hand, there are already "do-over" spells in the game. The first one the players will encounter is the Revifify spell:
Material Component: diamonds worth 300 gp, which the spell consumes.
You touch a creature that has died within the last minute. That creature returns to life with 1 hit point. This spell can't return to life a creature that has died of old age, nor can it restore any missing body parts.
The idea is you use this spell at the end of a fight on anyone who has died. You must prepare it in advance and it is expensive to cast. So you lose money and you have one fewer spells for that day.
If one of your players is worried about dying, then feel free to award the party some 300gp diamonds and let them decide whether to save them for Revivify, or sell them and buy that +1 flaming longsword.
Only Cleric and Paladin can cast Revivify. Of course you can change that rule if you like, or award a magic item that allows anyone to cast it. But keep the material cost.
When it makes sense from the fictional conceit of the fantasy world
The main way that I could see adapting the standard approach to D&D to accommodate removing character death would be to establish that as a core conceit of the campaign milieu. For example, one could establish a game world where the characters are being testing by the gods. Then, when the party fails (dies) sufficiently badly, the gods running the show might re-set the party in one way or another. Once you imagine the fiction that makes it so that the characters never really die, then that can be used to structure the mechanical aspects of when/how characters do get to checkpoints other artifices for recovering from or eliminating character death.