My character is a gunslinger bandit who's primary source of income is robberies. My usual MO is to go into a shop and have Sogg and Virgil beat the shopkeeper almost to death with lead pipes, then I give Sogg an axe and have him break open any locked containers while I pickpocket the unconscious shopkeeper and take all his cash. I haven't raised my pickpocket skill at all, but with the victim unconscious I can just try as many times as I need to.

Usually after I do this, the shopkeeper doesn't come after me when they regain consciousness, they just stand in their usual spot and say things like "Help! Help! Help!" When you try to speak to them. Every now and then though, you run into a character who will just keep trying to fight you until you kill them, no matter how badly you curbstomp them

So I guess my question is, why is that? Is there some stat or something that makes certain characters always fight to the death? Do all characters have some kind of a threshold beyond which they try to flee?

Do you mean that random characters just attack you with no reason?

I think he means that he has his thugs beat up shopkeepers until they're unconscious, then robs their stores. When the shopkeepers wake up, some of them just call for help, but some of them attack and fight to the death.

I'm not sure why they would behave differently.