I doubt the HP fandom will die down any time soon. :) There's still stuff to get excited about (movies, the wizarding encyclopedia thing, conventions, the theme park...) -- fandom just goes through phases sometimes. A lot of people sign up for exchange fests too, so plenty of people are probably taking a break after past fests, or focusing on their next hd_holidays projects right now, or getting ready for NaNoWriMo or something.