I just played thought this not 10 minutes ago, trying to save Captain Grisly and the others too, but couldn't manage to keep them alive. Throughout the fight there's some dialogue about removing the masks when they make their Saving Throws so that lead me to a strategy of doing non-lethal to them to knock them out, then looting the masks off their bodies. However the moment I removed the mask from their inventory, they instantly died.
Missed the Help the Hag Survivors quest though so maybe there is an option for a different outcome.
