At the risk of being a bit spoilery, just to give you a heads-up, the access you get later in the game depends heavily on your decision in the related quest. If you complete the scenario one way, you will be locked out of there forever, in which case you should make sure you have absolutely everything you want out of there before you exit (don't forget to pinch the bobblehead from your father's office). However, if you complete it the other way, it will remain open to you at all times.
I just won't say what the quest involves, or which way triggers which outcome.
One thing I will say, though; I had a hell of a lot of fun doing that quest as a bad guy.