I'd take Dad from Fallout 3, Dog from HL2, Atton Rand from TSL, and the main character from Fable 2.
Why?
BECAUSE NONE OF THEM WILL JUST FUCKING DIE.
I mean, srsly, Dad's essential, Dog just won't fucking die, Atton gets knocked unconcious or whatever you call it and he has the ability to get back up as long as he isn't the last standing, and the main character from Fable 2 also gets only knocked unconscious.
Come to think of it, why am I going as well?
These guys can handle it, hell, why don't we just send one of them in? I can guarantee that any one of these could do it with ease all alone.