Do summoned creatures die when reduced to 0 hit points?

Question

Imagine that the conjure animals spell has been used which includes the following text:

[...] Each beast is also considered fey, and it disappears when it drops to 0 hit points or when the spell ends [...]

In the comments to this question about homebrew spells the following was stated:

Looking at all summoning spells: They have the line "Each beast is also considered fey, and it disappears when it drops to 0 hit points or when the spell ends." This means they do not die [...]

I'm wondering if this is actually the case, when a summoned creature is reduced to 0 hit points has it actually died?

I would like answers to assume that summoned creatures do not make death saving throws (otherwise they wouldn't be dead and would disappear to go make their saving throws and it gets somewhat messy).

Also note that this is specifically about summoned creatures as they have the rather unusual behavior of disappearing when dropping to 0 hit points instead of the usual thing that monsters do (staying put). I'm unsure if there is something in the books about whether they count as having died when doing this.

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An example of where this matters is the Hexblade Warlock's Hexblade's Curse feature:

[...] If the cursed target dies, you regain hit points equal to your warlock level + your Charisma modifier (minimum of 1 hit point) [...]

Would they gain this benefit when a summoned creature is reduced to 0 hit points?

Answer 1

General rule

The rule on Monsters and Death states:

Most DMs have a monster die the instant it drops to 0 hit points, rather than having it fall unconscious and make death saving throws.

Mighty villains and special nonplayer characters are common exceptions; the DM might have them fall unconscious and follow the same rules as player characters.

Specific rule

The conjure animals spell description says:

... it disappears when it drops to 0 hit points or when the spell ends.

We'll take it as read that the animals summoned by Conjure Animals are not "mighty villains" or "special nonplayer characters" so that, by the general rule, they die at 0 hp.

General vs. Specific

So the question is does the specific rule replace or supplement the general rule? If the former, the creatures do not die, they just disappear. If the latter, then they die and disappear.

Either reading is possible but I lean towards the idea that it supplements - that is, they die and disappear. I do this for two major and one minor reason:

1. It's the plain meaning of the words - "it disappears" doesn't modify anything else that normally happens. Contrast this with the second paragraph of the general rules above "... are common exceptions" where the exceptional nature is explicitly called out. Or the vampire's Misty Escape "When it drops to 0 hit points outside its resting place, the vampire transforms into a cloud of mist (as in the Shapechanger trait) instead of falling unconscious".

2. It just gets too complicated the other way. For example, the Warlock's Hex and the Ranger's Hunter's Mark cannot be retargeted unless the current target dies - these are major class features that would be nerfed by the other reading.

3. It leaves a nice, tidy battlefield afterward. Field Marshal Montgomery was very keen on this.

Answer 2

By RAW, dropping to 0 hit points doesn't automatically kill you.

If you are not playing with any houserules, then this question can easily be resolved by reading the rules regarding what to do when hp is reduced to 0.

As per the combat rules:

When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections.

Instant Death Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.

...

Death Saving Throws Whenever you start your turn with 0 hit points, you must make a special saving throw, called a death saving throw, to determine whether you creep closer to death or hang onto life.

...

Roll a d20. If the roll is 10 or higher, you succeed. Otherwise, you fail. A success or failure has no effect by itself. On your third success, you become stable (see below). On your third failure, you die.

In short, when you hit 0 hp you could die from instant death, otherwise you have to start making death saving throws at the beginning of teach turn or after 3 failures you will die.

Once you understand this, there isn't any contradiction or rules questions remaining. There is nothing to say that a dead creature can't disappear or that a creature about to disappear can't die.

Consider the following cases concerning a summoned creature with 2 max hp.

1. The creature takes 1 damage: their hp does not fall below 0, they remain alive and summoned.
2. The creature takes 2 damage: their hp falls to 0, and they disappear.
3. The creature takes 4 damage: their hp falls to 0, and they disappear, but the damage remaining after reducing them to 0 hp is equal to their maximum hp, so they instantly die.
4. The spell ends: the creature disappears.

I see you are playing with houserules that state that enemies die instantly when they hit 0hp. If you are otherwise playing by RAW, then you should consider situation 3 above. If there are more houserules to consider, please let me know or have your DM resolve the situation.