PF2 has some tools (mostly different applications of the VP subsystem), but it’s a bit lacking on the GM-side of things.
Sure. It's the skeleton that is valuable to me, anyways. Gives me something to play with and manages to solidly attach itself to the players and their characters, but can do with me being situationally loose with it when I feel like it. As I've said before, it basically does what I was already trying to do with 5E, but without me having to create it from whole cloth.
It’s easy to fix, even if it’s just by not having everything react automatically with murderous intent.
Exactly. A lot of the problem here is that GMs assume that if they have the advantage, monsters will simply kill off everything and everyone through attrition rather than backing off, taking what they got, and/or simply driving them off. While wounds might just be numbers for players, they shouldn't be for the characters and their enemies; things don't like being wounded and hurt.
For example, if you attack an animal that is much tougher than you and manage to wound it, it strikes back hard enough that it forces you to think twice and back off. However, it doesn't follow and in fact runs off itself; the animal isn't interested in a fight right now and would rather stay lightly wounded than continue a fight they might win but at cost. Or maybe it chases and aggressively howls at you, but doesn't attack because it's more interested in you getting out of its territory. These sorts of results are totally understandable and make animals who are specifically
not like that (Owlbears come to mind) much more interesting and dangerous.
If you have an organized or an intelligent enemy, maybe they force the party to retreat but hold up to reorganize and deal with their own dead and wounded. They can certainly attempt to track down the players, but it's totally understandable to hold their own position and try to heal/recover who they can and bury who they can't. If they beat the party solidly, they can also always take hostages/prisoners depending on how they function. They might interrogate them, impress them into service, loot them, or maybe make an example of one of them. There are a lot of options, and none of them are system dependent: these are things that need to be done because if they aren't, any system can fail. And the second half of that...
Now training the PCs to do the same ….
... is this. And I think it's not even that players will always attack everything, but the bigger problem is that no one ever wants to leave someone behind. It goes against so many cultural and storytelling instincts that it just feels
bad, but it's something that needs to be an option. Too often a TPK happens because someone got into a bad/stupid/unlucky position and just gets
got, and then the party descends into the depressing depths of the sunk-cost fallacy trying to save them.
Having a player or two die in a sandbox campaign should
totally be something that happens, because it instills the right level of danger for a campaign where you can go anywhere. The problem is that everyone has a "One for all, all for one!" mentality when it comes to getting killed. People have problems retreating when someone gets left behind, and that's a system-less problem. Everyone needs to internalize the classic Neil McCauley quote: