well, i mean, there are only so many places he could have gone - your first (and to be fair, only) hint is the dead magisters on the west part of driftwood (provided you hadn't already killed them). at that point, it's just a matter of looking in that general direction
i agree that it's not a terribly well laid-out quest (if there was ever a thing to that tile puzzle to open the door, i never figured it out, but i never gave it much effort anyway so), but i didn't mind it too much
