What worked for me (after a few hours of trial and error).
After the cutscene of Lödwyn monologuing and the eruption, if she stays frozen and you can push her around, make a save (hard save, not a quicksave) and then jump off the cliff.
After the battle, if the quest doesnt ‘end’, go to the southernmost outcropping of the mountain, where you would find the Arrows of Slaying (?) for the Galawain Totem and a chest. If you use the ‘Severed Branch’ ability or some speed-increasing item, you can just barely manage to leap to the scaffolding on the other side and leave the ‘No Fast Travel’ area.
Then you just fast travel to the Quarry Beacon and the quest should continue as normal!
