[Felix Nephthys]

The way I always understood it was that the game didn't differentiate between killed, wounded, and troops that for one reason or another are simply incapable of fighting any longer. Troops will disperse at times which means that the ones who are left simply ran away. And, sometimes, they will surrender. I for one feel the game models these things pretty well already. As for a prone to surrender switch, I'm not sure what that would do that can't already be accomplished with the selectors in the Preferences menu. As for a leader being killed, that will already reduce the chances for subordinate units to rally which will increase their chances of retreating/routing.