Well, that all depends. If the entire trap is inside the skull, it would be pretty difficult to disarm. Honestly, I'm more interested in finding out what the trap is than in getting that gem, but no need to kill any party members over it.
*Cugel will double-check to make sure that the gem in LEFT eye-socket is not trapped. If it isn't, he'll stand on the RIGHT side of the skull, have everyone else move a comfortable distance away, and (while staying off to the side) pluck the gem from the LEFT eye socket.*