Can we see the map? I'm unclear as to where we go from here...
I should have posted one already. I'll try to get to it soon...
To be clear, although I may be misinterpreting what Dorgath means, the party is not truly stuck. Every room you've already visited is still accessible. The only remaining pathways you've discovered but still not explored are the locked door in front of you and the door to the fountain chamber, blocked by a magic barrier. Both of these do present some resistance, but...
-Tomas detected two magic power sources controlling the barrier. One of them is the green icon of Nurgle on the end of the goblin staff that Throg is carrying.
-Locked doors can be opened with keys, some forms of magic, lockpicking tools, or just bashed down; but not all of those methods are available for every door (a door sealed with a magic lock might not be possible to open with regular tools, and a sufficiently strong and thick door may not be possible to bash). This particular door seems pretty ordinary, but I'd assume that if you did bash it down, everyone in the area could hear the noise. It would be like an alarm going off, alerting all of the denizens of the dungeon to your approximate location.