Hahah, sounds kinda fun.
He spawns there all the time for me now too, we got into a fight after i stole a certain horse from him. Though he seems to of completely forgotten that i did and beat him within and inch of his (immortal) life, and greets me warmly every time i walk past him
If they're going to make NPCs immortal at least make them remember that i've most likely ruined their life.

It has slightly ruined the game for me to be honest.

Just make it like Morrowind, if you kill someone that is involved in a Quest, something comes up on the screen telling you so if you want to load an older save you can. What is so hard about that.

especially when they simultaneously greet me

I just hate killing someone for a soul trap and them waking up...

Have you actually done any programming? So programming a simple ifelse statement is a programming nightmare? They wouldn't have to make the damage different at all. The game already differentiate player and npc hits when it comes to companions (insteading of companions going on one knee, they get killed instantly by a player), so it wouldn't be that hard to do this.

they are stupid beyond all belief. there is a certain questline in markath that involves a bit of fighting and there were four immortal town npcs that got involved and the battle simply wouldnt end. i ended having to reload and wait somewhere else so that the story could continue on. either put them someplace where they wont get hurt by other npcs, or have them knocked unconcious for a couple of hours or something. the way it is now is just stupid. and what happened with if someone dies the quest is given by someone else?

That's one of the funniest things I've read in a while.
What a life, just staying at some dude's house, and trying to beat him to death every time he comes home.

I had forgotten about that. a little unimmersive, but better than the unkillable guy.

I also like the idea someone else said about them staying down for like an hour before getting back up.

the player should be given to freedom to kill these characters

Skyrim needs it's immortal NPC's and not necessarily because of the player. Skyrim is unpredictable I wouldn't want Esbern getting killed or some other important NPC getting killed by a Dragon. Maven Black-Briar is the exception she shouldn't be immortal or rather their should've been a quest involved where you can take her down.

It's a fine system and a necessary evil, I just wished they keep the essential markers from Oblivion, if I had a complaint about Immortal NPC's that would be it.

Essential NPC's should come back from the dead to be used in quests their needed. Other than that they should stay dead. But having them not killable really screws up my killing sprees.

Oh thank god. Post limit. Honestly people.