Ebb, stealth may be another option, given that you have several unique physical properties of the plane to take advantage of. There are paths while remaining within the spire that lead out of the chamber, or as you pointed out, you could brave the outside. Diplomacy is almost always an option in Planescape too. Even the bluntest of individuals on the planes knows a bit of philosophy, and even races that normally aren't negotiate may end up being so if you approach them the right way or figure out what they want. Alternately, you can try your luck with the bugbears instead.