Hello Amagikarp, can't you teleport one of your characters into the cage? (Preferably NOT one of the npcs if it's a damaging teleport, that tends to upset them.)
If not, I hope you have a save game from right before the fight (most important fights have an auto save before them). In any case, you learned not to put potential item bearers into indestructible cages … you have my sympathies.
