There are two potential problems:
1. As Senka said, without a thief disarming traps, you are dead.
2. I am not sure it's possible to continue to Athkatla without Imoen in your party. Although, I suspect that in this case, another Imoen would be summoned in the cutscene with Irenicus, which makes the whole plot really stupid, in my opinion. How can you leave your *lil sis* in this terrible dungeon?