If I remember correctly, this also includes the player character. If you are struck by a hefty blow to an unprotected body part and fall, you´re likely to die but if you get knocked out due to stamina damage, you are just that - knocked out. What happens to you while you are unconscious is up to the NPCs which defeated you. Some will simply finish you off, others may just take your stuff, capture you (?) or leave you alone.
Maybe it is als influenced by surroundings. For example, if you are in the wild´you are much more likely to simply get off´ed, while when you are in a city with actual authorities that keep order and persecute people this would be much less likely.
Yeah, I also think things that make npcs feel real, is that they feel flawed in some way. And by that I mean make decisions that don't really make sense sometimes. for example,
-A brave villager stands to take you on, with nothing but a rusty pitchfork. Not because he was programmed this way, but because his opinions, personality, and feelings towards you are so strong.
Or
-A knight in shining armor cowers before you, Even though you're only wielding a short-sword, He's heard tales of the things you have done, and thinks twice before engaging you.
Or
A group of bandits decide to jump you one afternoon. They have not heard of you, but your posture, confidence, and bravery is enough to make them back down.
Or
You go to a local tavern for a drink. An npc forgets to charge you, But thanks you when you remind her.
It's the little things.