[Faceman]

You do not necessarily need a thief even without cheese (i.e. knowing trap locations beforehand).
The two essential skills can be substituted by a divine spell (detect trap) and an arcane spell (knock). However this IS a pain in the rear end as Six correctly points out since you have to waste some spell slots on them and rest every time they're used up.
Without "Knock" you can still Bash most (if not all) game critical doors and chests by drinking giant strenght potions or wearing strenghth improving equipment.
Also there are only a few traps that will insta-kill you (regardless of current HP) and you could always have a summon scout ahead.