For the people who reach the bottom of the cave and find Maryina "unresponsive", there's a trick to work around the bug and unlock the rest of the quest.
You have to throw some AOE near the control orb
on that small wooden plank, where the hag is hidden in invisible mode, to make her appear and trigger the fight.
P.S. I generally liked this questline a lot, but Jesus Christ if I didn't hate with fierce passion that part with the poison traps after the masked guys.
A perfect marriage of shitty design and a horrific control scheme.
