Well, back in the day we had the "Fighting to the death" morale status in game. If a unit was literally surrounded and had no escape route, they would just fight until the last. I think their combat stats were lowered in that stance too. I don't know if it can be implemented in this game, the last TW I know of that had this was Medieval 2. Since then, the game engine changed so I don't know what to say..
I miss that stance myself, sometimes you can see a hoplite formation being surrounded that just decides to break and run into a wall of spears. Don't think it happened that way in reality
