that after you nuke Megaton what'shertiks Brown goes to underworld. I just strolled in to speak to Mr. Crowley and there she was, ready to give me the quest line for "The Wasteland Survival Guide"

ok, carry on.

Moira Brown would be in Underworld, but she'll be a ghoul. When the quest is completed, she'll go to Megaton Ruins.

Yup. After you destroy Megaton, and go there, afterwards, you can find Moira as a ghoul, and she'll say she's on her way to Underworld. On her way, I followed her, as she passed Super Duper Mart. Well...we sorta encountered some not-so friendly raiders, who tried to blow up, the big bus, near the Mart. It was ready to blow. I guess I was the only one who could see the smoke, because before you knew it, Moira was flying over my head, when the explosion deploded.

Hope you got the bobblehead before blowing up MY TOWN! Wait, I mean, I hope the bobblehead lies buried in the rubble! LOL

I was SO PISSED!!!! I wish I could make this up.

Ok, so I have every single bobblehead EXCEPT for megaton. I seriously spent all day collecting them (I had 0) and after 4 or 5 hours it was time to go to megaton and get that one. Well, I blew up the damn town so all that time spent was a waste It does in fact lay in the rubble somewhere.

What makes it worse, I play on xbox360 and that is the very last achievement I need to get before completing it 100%

LOL well, now you know that every evil deed has its consequences! For shame! Blowing up Megaton. -.-

Guess you have to start a new game. Heck, at least you know now what you have to do!