[Hopeless]

Does this party of yours have any npc's?

Its just that from what i recall from the novels the most likeliest outcome is the Daekyr possesses one of the npc' and returns with them with noone the wiser.

Then its just a waiting game since once free it can possess whoever slays its current host until it finds someone "suitable".

Sorry that doesn't help with planning what to do once they're there I figured I ought to mention a possible outcome and who should be effected as i picture them fighting off their foe and "he" slips into the ocean and disappears causing the island to start sinking as well, as a bright light at the highest point on the island beckons your players to rush through before they sink into the acid ocean along with the island...

Dramatic licence to hide what should be an ominous threat for a future game!