Of course, you can. The game's not Fallout 3.....
But it wouldn't matter anyway, because....
they once maked that mistake in Fall Out , not soon after that they did have a DLC wich covert that up ...
....it wasn't a mistake in Fallout 3, I played 50+ hours after "finishing" the main quest, without the DLC. And that DLC
was the biggest mistake they made, since it screwed up FAR more than it "fixed".
(Broken Steel was aptly named, since it just broke so much about that game.)