When I had arrived at the observation deck and activated the portal I noticed Sally and the other NPCs were gone. I went through the previously visited locations and couldn't find any of them.

Might Sally have been accidentally killed by aliens or maybe proximity mines?

If so, anyone who knows how I can re-spawn Sally so I can continue in the game, as I think she needs to unlock a door.

Any help is much appreciated.

What system? And kids can't die in Fallout 3.

And finally, if you figure out tell me.