Lanefan
Victoria Rules
Another mechanic here is that if someone goes to or below 0 h.p. (and negative h.p. are essential) they need to roll under their Con. modified by their current h.p. on a d20 in order to remain conscious. We've been doing this for ages.As a simulationist, I really like the implications of your variant. Don't want to insert it into my existing campaign, but would consider stealing it for a new one. I like the fact that it makes it possible for people to bleed out over long periods of time, and I like the fact that, as you say, it makes sense to just leave unconscious characters/monsters alone until the combat is won, and then you go around cutting throats if you are so inclined.
The one modification I would make, if I were to using this, is to have a narrow band of HP (say, 0 to -Con) where you are incapacitated but still conscious until you fail at least on death save. This supports the narrative trope of e.g. finding a wounded warrior who gives you information before he dies, unless you heal him.
Another variant to consider is that if someone goes to or below 0 h.p. they can only be cured to - let's say 10% of their usual total - before a long rest. If while still incurable this way they go to or below 0 h.p. again their "curable lid" is one (or two?) points lower; and if the curable lid ever gets to 0 the character dies on the spot due to accumulated wounds (if not dead already, of course). Yes this means a character can be down and back up a few times in a fight (or over the course of a day) but one hopes they'd be more cautious in order to avoid this death spiral.
Another argument in favour of negative h.p. is knowing how mangled a corpse is plays into whether it can be Raised or whether something more powerful is required.
Lan-"I'm an expert on death - I've been there and back again far too many times"-efan