How about a ransom and if accepted, a negative trait? Persons of importance could be captured instead of outright killed, ransomed based upon some calculation of their worth (XP, items, etc.), and if the ransom is refused, executed?
[Edit] Let me clarify further:
If a champion reaches 0 hp in a tactical battle and his/her side wins, he/she doesn't die but instead needs to take a random negative trait and/or stat reduction such as -1 to constituion or something similar. If a champion is wounded and then his/her side flees, he/she is captured, held for ransom, and if ransom refused, executed. Certain monster types such as spiders would never hold for ransom - not enough intelligence for that.
If a champion reaches 0 hp in a tactical battle and the opposite side wins, he/she is captured, held for ransom, and if ransom refused, executed. Again, ransom is determined off monster type or intelligence check.
Just thinking Game of Thrones type thing: if an important person is captured they are held for ransom/gain.
[Editx2] Instead of automatic execution if ransom declined, maybe, depending on the opponent, champion can change allegiance to spare his/her life. For example, I lose a tactical battle to an enemy AI. Ransom is demanded, I refuse or am incapable of making payment. Champion decides to switch allegiance to spare his/her life.
[Editx3] Could introduce a 10% chance (or some other value) that if a champion reaches 0 hp they die thereby leaving no chance for capture/ransom. With that said, could introduce a positive trait to champions where if they are mortally wounded to 0 hp, it reduces the chance of death to 9%, 5%, or some other value. Call it survivability, battle luck, or something similar. Could also consider a charisma check that if captured, enemy never executes the champion.
Just thinking out loud here.