I don't think so. I don't know any thing about the Harry Potter clubs, but the Twilight 俱乐部 seem fine. They're not as active as they were a couple years ago, but they are very far from "dying".
(It would be wise to actually look at Twilight 俱乐部 before concluding that they are all dying because "Twilight is just a phase")
I can only speak for HP, and we still live and kicking so to say. ;D and when 你 say here, do 你 mean fanpop? because when it comes to HP fandom we mostly play in LJ, AO3, and tumblr... in tumblr we are starting a new role play game. and this november there are new fanfic festival going on. well, in 潮流粉丝俱乐部 the goings on are definitely less compared to when the movie still going on. since not much we can do here other than 民意调查 and answering 问题 that has been repeatedly asked.