On a character I have Mister Sandman, and I killed every unnamed NCR soldier who slept in the Mojave Outpost (and then positioned them around the bar, making it look like they were very very drunk) will they ever respawn or will I get the chance to recreate my monument to sadistic boredom?

Indoors people don't respawn. (That's how it was in FO3 at least.)

I think generic unnamed NPCs respawn and ones that are 'named' dont with the exception of

I think you have to go do something else for a week of game time then come back.

I always go to the same outpost for ranger veteran armor.