Once you have confronted Dr Elrath with the evidence from his cellar (don't forget the cure potions), report to Commander Ralph (south of Stormfist castle) to complete the quest.
If you finish any of the quests which give you an invitation to the castle, the healers will automatically move on their own and you will be unable to complete that quest. If that quest log entry is not marked as failed, I guess it will just stick around until you perform the blessing ceremony and the quest log gets cleared.
