Some games have it all set to determine when people flee from battle. They have some manner of morale check and then go scampering off. We intentionally avoided writing specific rules for that because too often players will tailor their characters to force those morale checks and then they never have to fight. You have to fight sometimes in a role-playing game (even though we constantly harp on making it a role-playing game and not just a battle system).
But what do you do about it in game? Earlier this week I was running a game where the elven bandit was at half his Life’s Blood (hits to kill) and facing two warriors by himself (his partner having been killed the last turn). Does he run? They killed his buddy, they hurt him, how much does it take? Well Legend Quest has a Willpower attribute, so I forced a Willpower check on him to see if he would stick it out. He passed the Willpower task, but I still had him start walking backwards - fighting retreat. #1 - He had allies back there, including a sniper who was hidden. #2 - I just couldn’t see a light elven bandit standing toe to toe with a human fully armored knight and a half-orc killing machine.
So when does it happen? Too often, it never happens. Characters (both player and non-player) stay in combat until they die. Are we really that stupid? Shouldn’t there be a point where you understand that you’re going to lose, at least that you’re going to lose here? Shouldn’t you then retreat, either get out of there completely or go find a better spot to fight? Well, if the game rules allow the enemy to have a freebie hit against you, then I understand why you don’t run - running could get you killed.
In Legend Quest, one of the best ways to run away is this: You let the other guy take his attack. Chances are when he tries to hit me, he is not going to take a negative for a “walk modifier”. Well, that means that he cannot walk this turn. (Characters in LQ can always “free walk” but this is usually 5-7’, not 30’+.) Now, I can take a walk modifier and walk backwards. I might even hit him as I’m retreating. Smart teams will have wanted to put an enemy behind me to stop me from doing that, but they may not have had the chance yet. With this rule, an enemy often has a chance to retreat without getting killed.
But still - When? The reason I don’t want to put numbers around it is that I think it is entirely different for when a bandit flees vs. when a soldier flees, and not only because of their Willpower, though that is also a factor. I think as a GM you need to know this type of thing when you create the NPCs to fight. Are they religious fanatics? They never run. Are they soldiers who feel a sense of duty? Are they bandits or mercenaries who care only about profit and expect to stay alive? And if they consider running away to be a perfectly normal course of action - Do you prep them by giving them some sort of advantage? Does the spell caster have a fog or obscurement spell? Does the horseman have some caltrops? Does the thief have a potion of invisibility? And if they do (have a means of escape) are your players and their character smart enough to recognize that and take advantage of it when they meet the next patrol of enemies?