@ Djcd - I"m sorry, but the rule of thumb that J Mods have applied in the past to similar situations, is that when you create and post content for a particular clan's thread, it is considered to be a gift to that clan. If you leave that clan, for whatever reason, that clan is still allowed to continue to use the content that you created for them.
If you do not wish them to use that content, that becomes an issue for you to work out in-game or private conversation with the current owner of that clan. It is not an issue for the Forum Moderators.