I play AD&D by the -10 rule to allow for PCs to bleed out before death. Most battlefield casualties come from blood loss. I have spiced it up a little, though, as PCs lose 1d4 hp per round once they're below zero, not just the standard 1. The real question is, what does this mean for NPCs and monsters? Should they simply fall down dead at 0 hp? Is that likely, desirous, or even fun? No. After playing the excellent playtest rules for Feudal Anarchy (aka Medieval Hack), I have been convinced of the utility and wonder of finding dismembered, bleeding, badly wounded, or unconscious NPCs at the end of a battle. So what is my system for determining if someone is dead?
Currently, I don't have one. I simply let my whim decide if an orc that's been skewered is dying or already dead. This seems to me to be a rather haphazard and, if I may say so, arbitrary way of figuring out if the great lord the PCs just skewered is in his death throws or if they can take him captive and use him as a bargaining tool. The simple fact is NOT EVERYONE TOO WOUNDED TO FIGHT IS DEAD. In fact, generally, in most medieval warfare, those too wounded to fight are rarely dead.
I normally just record foe hp and then cross it out as the foe is damaged. This new proposed system will add marginally more work to that method, but I believe it will (compared to the work added) greatly increase the complexity of player choice and interaction as well as the realism of any given fight. The system I propose is as follows:
If an NPC is reduced to 0, they have a base 10% chance of being mortally wounded at the end of combat.
For every point below 0 they are reduced to, this chance is increased by 10%.
All NPCs below 0 hp will need to be tended to by a healer. In order to recover a character who has been non-mortally wounded, the healer must make a healing prof check. This check suffers a -1 penalty for every ten minutes since the battle has ended. Each attempt to heal a dying man takes ten minutes.
Gilberte, Francis, and Hadrian are fighting the men of the Count de Coer. There are three foes, all of whom are downed. One man is reduced to -4hp, another to -8hp, and the last to -1hp. These are 50%, 90%, and 20% chances of being mortally wounded respectively. When the PCs check on the dead, the DM rolls... 19, 27, 76. The first two men are beyond saving, dying messily. The last is not mortally wounded, but will require a healing check to stabilize. None of the men were necessarily unconscious (that's up to the DM). This last man can now be taken as prisoner.