In some TW games this is slightly modeled in, in the sense, that a unit might choose to fight till death, rather than running away, when they are surrounded and

In some TW games this is slightly modeled in, in the sense, that a unit might choose to fight till death, rather than running away, when they are surrounded and they have nowhere to run. So then you open up a way .. and they will try to run again, which is easier to finish them without own casualties. But those are hardcoded algorithms. The units do not really learn. (that would be awesome, but is very very hard to implement in realtime in a proper way) They just improve their stats with experience. So they get stronger in stats in either case, even when fleeing every single battle.