Wait what.. i never though of this but....
is it possible to kill every NPC inb the game?? in a way that you never see any npc again?
You can kill many npcs and as such will not be able to complete some story lines.
But why dont you try gallopping up to the grey bards and go for a killing spree.
Tne write back here how you realize Bethesda thought of this and made some NPCs immensy powerful, as they should be, and your [censored] was kicked.
I dont think you can anihilate all the NPCs but pretty much most.
I would say that before you are 10% through, your reputation and bounty will be so high that you will have endless hordes of soldiers chasing you, and as such, will die so often, you simply start over.
So all in all, although in theory it might be possible, in practice, I think its impossible since you would die trying. And thats how it should be. Cause someone performing such actions should be killed, in the game that is.