Two years ago when I was in Marleybone I found two ways to get to Celestia.One gives you a key, the other you have to fight in a tower like Briskbreeze for the key.(I think you know which one I chose)I still wonder if I beat that tower will I have to redo Celestia?
The quest from Halston Balestrom that sends you to a difficult Marleybone tower was part of the Celestia preview only https://www.wizard101.com/game/community/updatenotes/july2010 It is not necessary to complete this task to gain access to Celestia, and completing this task will in no way impact your progress.