Two characters helped immensely in our party.
My character was a Monk, with maxed tumble, jump, hide, move silently, and diplomacy. In combat I would mix it up with opponents, or deliver curing potions to the wounded. Diplomacy helped out with convincing guards to let us pass. (With suitable bribing) To my credit, I never died during the entire module. Came really close a bunch of times, but never all the way there.
The other character was a social/scout rogue, who would get us through and helped sow discord among the different temples in the mines, as well as convincing a delegation of the fire temple to accompany us in the fane. Diplomacy, bluff, sense motive, Use Magical Device, tumble, hide and move silently were the keys to her success. She died in a fight late in the module from a destruction spell.