Okay so, am I the only one getting annoyed with these npc's that cannot be killed at all? for example, I'm inside the thieves guild after getting chased inside by guards ( I don't think they should even be able to enter this area. ) but there's this one guy which I'm guessing has to do with a quest or something but... he can't be killed at all, its frustrating that every few seconds the guy gets back up and starts fighting again. I cant even talk to the people in the guild because they constantly attack him. I've tried everything i can think of. I've tried, leaving the area and coming back, using a fear spell on him, and simply hitting him until he leaves or something. but no, he's still in there constantly fighting which is causing me not to be able to do any of the quests for the guild. so what I'm proposing is that "immortal" npc's that don't have anything to do with the main story quests can be killed, or they at least flee the area. ( I would've reloaded the save but my last hard save was about four hours ago and i've turned off autosaving so my save file doesnt get any bigger and cause even more lag than the game already has.)
Fast Travel to Whiterun
Sleep at your house for 3 in game days, not 1 hour less.
Go back to Riften. He shouldn't be there anymore.
-And yes, immortal NPCs svck, and I totally agree we should be able to kill anyone not connected to the MAIN Dragonborn quest line.