I have seen several threads about the point that Wizard101 went downhill, the thing that caused so many players to leave. The popular belief is that it was with the release of Celestia. I am convinced that the worst thing that has happened to Wizard101 is...
Just think about this. It has caused so many players to leave Wizard. Unfortunately, KI doesn't care about this because they're still making money, after all.
What I think is the worst thing that could happen to Wizard101, and might even bring about its end, is the release of a third game. Currently, there are players that play both games, Wizard-only players, and Pirate-only players.
There will be players of both games that decide to leave Wizard in favor of the new game, while continuing to play Pirate. There will also be Wizard-only players that will leave for the new game.
Kingsisle's next game release will definitely reduce the number of Wizard players. The question is - does it need to be a "101" game to lure them away, or simply one made by Kingsisle?