In Morrowind, it was possible to permanently kill NPCs who were involved in the main story. This would result in a message basically informing you that you had broken the world and to reload a save if you want to make progress. In Oblivion, this was changed so that important NPCs were "knocked out" instead of killed.
In Skyrim, is there any (outside of console or game file editing) way to permanently kill an important NPC or can I go on a killing spree relatively care free?
Best Answer
Important NPCs are invulnerable, like Oblivion.
You might close off some smaller sidequests, but the folks necessary for the main story (for instance) have a tendency to be "incapacitated" from "killing" blows.
So feel free to go nuts.
Interestingly, NPC allies behave a little different, even if they are non-essential (and thus ripe for killing). When they get reduced to below 0 health, they revert into the "yield " state, which usually means enemy NPCs stop focusing on them to come after you instead. If they get hit while in this state, they will die.
Additionally, you cannot put them into this state - your attacks will directly kill them.