I was looking for the old discussion about this but was not lucky enough to find it.
In my opinion the “Total War” way would be the best and most fittig. All Enemies are broken/ fleeing? Get a popup that lets you choose to chase them or end the battle. If you choose to fight on and later see you won´t get them you should be able to end the battle at any time. For this simply change the retreat button for an end battle button after you got the popup.
"I am a Paladin!"
>OMG, Malthus, there are no damn paladins in Battle Brothers...<
"OK, OK! Then I´m a wrecked down minstrel drunkard pretending to be a paladin, singing so wrong in the midst of battle that even the undead run in fear... Better?!"