[He shrugs. When you explode whole towns on a regular basis, blowing up a dome this size isn't much.] With a few precautions in place. I know a spell that protects people from water and would keep the pressure at bay. It would take a lot of energy but between us we could get everyone to the surface. [He thinks. This is theoretical of course, but why not sound confident since it's not going to happen?]
We don't know what's up there, of course, which is why I'd prefer to break the dimensional barriers and get people home that way. But that's failed three times now, and beggars can't be choosers.