Two death states would be weird in this game, as that would mean that potential prisoners have more survivability than your own mercs have in battle. Currently a death is a death, adding another death state would create strange situations where your own mercs are dead if you win, but might survive if they were captured.
You also have the problem of reliably getting prisoners, since the battle system has fatalities and you can’t exactly patch up someone who’s lacking a head or guts. You’d mainly want prisoners for the purpose of more quests and events, so if you can’t take the guy prisoners who you need for the quest then the system just becomes a source of frustration and save scumming.
