Actually....if Skyrim is going to be true to form as Morrowind was.
You CAN kill everyone and thats it for it.
The only thing that annoyed me about Oblivion is that you werent allowed to kill certain people who were questgivers and such
Which i thought was unfair, as we SHOULD have the choice to destroy our own destiny
This is supposed to be the greatest Sandbox game ever created.
Yes, it's true that you should have the choice. But it was done like that because maybe someone else could kill them. In Morrowind people didn't move, but in Oblivion they did, and sometimes, for some strange reason, they decided to atack a guard, signing their dead sentence. Suppose that Martin was killed by a guard, for example.
Anyway, I don't remember clearly if in Fallout there were assential NPCs, but if there were, I'm sure they were less than in Oblivion. Hopefully, the tendency will go on.