The party has recently lost its cleric (the player and the character). Supposing no one intends to switch character or heavily modify their build - even if there are some chances to retrain - what could be done to to make up for the lack of healing?
The party is not ENTIRELY devoid of healing, but it's really little. Here's the composition:
All the characters are level 9.
In-combat healing is rarely an effective use of resources, usually it is better to focus on hurting the enemy. In most encounters no PC goes down, and the higher your level the most likely it is that a character is "taken out" not because of lack of HP, but by being stunned, paralyzed or dominated.
So if the GM compensates for the 1/5 decrease of party power by weakening the enemy similarly (as he should), you will find most encounters no more challenging than before.
Hopefully someone already has Medicine at expert level, with Assurance, Continual Recovery and Ward Medic. These provide much cheaper out-of-combat healing than spell slots.
Of course if that someone was the Cleric, someone else needs to retrain into these.
If you want to use Medicine in combat, you can also take Battle Medicine.
Natural Medicine might look tempting if you have a high proficiency in Nature, but as shown above, you need skill feats to be effective, and for those you actually need Medicine at least on expert.
These cost money, and are even less action efficient than spells.
A Moderate Elixir of Life costs 150 gp (9.4% of the total expected wealth of a 9th level character), takes 2 actions to use (1 to retrieve, 1 to drink) and heals 5d6+12, which is barely more than the expected damage output of a 9th level monster in a round.
With the same 2 actions, the Wizard could cast a 5th level Fireball, or the others could attack twice, potentially reducing the enemy damage output (by killing the enemy).
You could buy less expensive potions, but than the effect per action decreases further.
For the same price you can buy a 5th level Heal scroll, that heals a respectable 5d8+40, but only the Champion can you need a multiclass to cast it, and takes the entire turn (1 action to retrieve, 2 to cast)
The Pearly White Spindle (Aeon Stone) is uncommon, but can provide 1440 HP healing during the day. More importantly, it heals you during the 10 minutes you Treat Wounds (or is done to you), and it tops you off during the looting if only a few HP are missing.
Many people like the Healer's Gloves, I never understood why. 2d6+7 HP is not much for 80 gp, and the +1 for Medicine checks is meaningless for Treat Wound if you use Assurance, which you should. It can be useful if you cannot use Assurance1, like treating bleed damage, but that is rare.
Its best use is on characters not investing in Medicine, so they can bring up one fallen PC once per day.
Blessed One gives anyone Lay on Hands, which is nice, but you already have one character with it. Better if you want to heal a lot to one character.
Medic gives bonuses the HP regained via Treat Wounds and Battle Medicine, and more frequent usage of the latter. Better if you want to heal some to more characters.
On level 9 Humans can take the Multitalented feat which gives you a multiclass dedication feat:
Any divine or primal caster can use Heal scrolls (which provide the most HP/gp) with just the Dedication. With Basic Spellcasting you get your own slots, but they are too little too late when it comes to healing.
Pychic provides another Focus Point which the Champion can use to fuel Lay on Hands.
The Champion can take the above mentioned Psychic dedication, but beside that there are other feats like Litany Agains Wrath that increase your Focus Point pool. Desperate Prayer lets you use it once more.
"One ounce of prevention is worth a pound of cure".
It is much better if you do not need your healing in the first place. Increase your hit chance (weapon potency runes), your damage per hit (striking and elemental runes), your AC (armor potency runes) and your saves (resilient runes).
A Ring of Resistance (fire) is easily affordable on level 9. A Greater Grim Sandglass costs more, and negative is less common than fire, but I still found it a good investment.
Of course it is not only about damage dealt, received and prevented, as control, buffing and debuffing is equally important.
I mostly play PFS, for this reason I cannot know beforehand what classes and builds I will be playing along. My characters need to be self reliant.
So most of my characters have Assurance (Medicine) and Continual Recovery by level 5.
Battle Medicine can reliably heal 2d8+10 by level 6 (Assurance + Expert), which is just 1d8 less than a Healing Potion of the same level, but is rarely used, as the actions are better spent elsewhere.
There are lots of characters with the Heal spell other than Clerics; primal and divine Sorcerers, Summoners and Witches, Oracles etc. Still, I mostly see only Clerics with Healing Font using it, as they cannot spend those slots on something more useful anyway.
I played most games (in PFS) without Clerics, many without anyone with Heal, and some without any kind of healing. There was no correlation between the amount of available healing and difficulty.
In PF2, Clerics are very powerful as they can spam Heals that can match the damage output of most foes you are supposed to encounter at your level. I have seen several groups rely a lot on this and being able to win fights without much effort.
If you aren't already, you may start playing strategically (I don't mean "with powerful builds", I mean by running away when the fight looks too hard, taking advantage of the terrain, exploiting the dumbness of some monsters, getting into efficient formations to trigger your Champion's reaction as often as possible...). If that's not your jam you should simply tell your GM right now so they can downscale the campaign's difficulty.
If you are already playing strategically, then you should be able to adapt. If your GM follows the guidelines there should be less monsters to fight, so overall you are not loosing raw power relatively to them. You will simply have to adapt to your new situation where you can't rely on a sudden full health refill on a regular basis.
It's been a while since I played, but I was playing an alchemist that I had themed after H.P. Lovecraft's "Herbert West", and since Herbert was a doctor in the story, I leaned heavily into medicine skill and took the Battle Medicine and Ward Medic feats and I was a pretty solid non-magical healer. It definitely took me out of doing damage, but by then I had my bombs doing DoT for me already anyway. Like I said, it's been a bit since we played our PF2 group, but I remember skill/feat-based healing being relatively effective.
