Fleeing is not an option.
Yes, it is. You complain about unreasonable NPC reactions, but the player
has to kill much weaker NPCs, because 'they started it' or they could hold a grudge than might possibly cause some inconvenience?
You can't just run away and then engage them as an NPC again.
Because that would be totally immersive?
Personally, if I wandered into a neighbour's house and started looting, a little old lady caught me and came at me with knitting needles, after running away (an arguably more reasonable reaction 'defending myself' with deadly force) I think I'd try to avoid her for a while.
You know, she could simply take her wooden spoon back and then refuse to talk to you again.
You mean like already exists in D:OS, depending on the situation, NPC and (primarily) your reputation?
