Hi
I've just played Fallout 1 for the first time and have really enjoyed it. I've spent about 50 hours, really took my time and done as much as I can with my character, until I accidentally finished the game what feels like prematurely.

I went to the Cathedral after upgrading my power armour and plasma rifle thinking that I was going to be taking out a human Master of the Cathedral for Nicole of the Followers, as a sort of side quest, managed to blastmy way through and ultimately killed the Master, got out and boom! Game over.

So I've since discovered that I totally missed the military base section, which I knew about as a Brotherhood Initiate and was kinda saving for end game. But now I've just ended the game anyway. I've read some guides and they seem to suggest both need to be done to end the game, yet my game ended at the Cathedral without ever seeing the base. So did I miss much? Have I finished fallout or should I go back and do it properly? I feel like I bypassed a major part without knowing what I was doing.

Wait what? The game ended as in credits and everything and you didn't destroy The Vats at Mariposa? You have to destroy the Vats and the Master which as you know are in two different locations.

But if you somehow managed to end the game without taking it out. You missed going to Mariposa and seeing the Vats and a chance to have a nice conversation with the http://fallout.wikia.com/wiki/Lieutenant

Edit: Did you have a conversation with the Overseer of Vault 13 where he tells you that you can't go back?

I'd say it's probably best to revert to an older save and do the military base, in-terms of story you know what's going to happen but it's still enjoyable to do and as styles said lieutenant is an interesting character to talk to

This doesn't seem possible.

When you say "got out"... Do you mean that you escaped the Cathedral and ran for your life far into the wasteland to escape the nuclear blast? Or do you only mean that you stepped outside of the cathedral? (If so it means your PC is dead).

You have to destroy the Master and the Vats to end the game; unless you divulge the location of Vault 13 to the Lieutenant.