Never heard of x-com? Well, I guess aliens != criminals.
Anyway, not married to the idea. Probably not even viable one if requires fundamental changes. Was thinking how to deal with puzzlement of lethal mode - not being lethal at all until it's the last hit. So the risk to put a unit on 'destined to die if downed' list is just one possibility, calling it internal bleeding is merely an example of implementation.
Naturally I would imagine being killed as default and if players want talk with subjects, be good and such, they need to be more careful. But you've turned the table and offered players a peaceful safe-space (mode), in a way it makes one more responsible for his actions. Intrigued, as it forces to think differently, makes me look more critically into the implementation, if that makes a sense. Not sure if contributing anything though, so don't hesitate to tell stop babbling.
Idea is that even if used non lethally, certain items might end up killing the target anyway (explosives being an example, or headshot with gun), with more dangerous weapons having higher risk of doing so. Bit wary of this, as don't want to substantially reduce the player's weapon choices if going non lethal.
Certain weapons (explosives) or approaches (lethal, headshot) not being a gentleman's way to fight? That's interesting indeed
The question was how exactly this chance works. For example, could throwing a grenade which wouldn't normally eliminate the target (eg. 6pt damage vs. 20hp enemy) kill him on the spot if it rolls right, or does it work as the lethal mode again - only the last hit counts (this time with a random chance at play)? Btw. the lethal-mode way makes it much easier to use at higher difficulties with such high HP increase of enemies.