Even though fandoms usually have to acknowledge canon I think there are a few exceptions where the whole fandom is allowed to completely disregard it and revoke it from its canon status. e.g.
- The “How I met your mother” finale
- Avatar the Last Airbender movie (which in fact did not happen)
- Dan Humphrey being Gossip Girl
None of the above actually happened and should be disregarded by the fandom. Have a good day.