Yes, people are juggling or (god forbid) migrating over to other fandoms (either the most popular or vocal being PoT, Veronica Mars, Battle Star Galactica, SGA or other anime/manga). Yes this includes BNF. Yes it can get harder to find the HP love through all the posts coming in now.
It does make me go "woe" at times- I mean sure, you can enjoy listening to the squees but...you can't exactly join in when you don't have the same intense love of the other fandoms.
I can't help viewing this movement- or phase- as anything but a good thing. It means new ideas, new thoughtstreams which leads to more stuff for the HP fandom. It might take a while but I'm kind of excited to see crossover/AU or just generally different HP fanfics that are influenced by ideals and imaginings from other fandoms. That would be all kinds of awesome for me.
And with HP, there are always new people coming in. HP isn't just a fandom. Its a freakin' cultural phenomenon. And LJ accounts for barely a *percentage* of the fan base. So we keep seeing newbies who decide to venture into the unknowns of LJ whether it's for fic, picture prettiness or squeeage. Then they get sucked into it. And with every book or movie, the fandom just explodes past its previous size. Its crazy.
I've seen fandoms last 10 years after the final piece was published - and that is pretty much on the *ordinary* scale. With HP...who knows? So, really, I can't see it 'dying' any time soon.
Instead what I do see is sort of a different era when it comes to fanfiction. BNF authors might not write HP stuff anymore. Fine. Yes their contributions helped shaped the fandom (and we'll always love them for it) but still, its not the end of the HP world. We have newbies who might just be brilliant authors in their own right. Some might need to work at their writing a bit more - others, just haven't been pimped enough. But there is that potential - and the HP fandom is never lacking in it.
If you're feeling a lack of HP squeeage in your life, don't wait around - do *something*. There are never enough comic strips, fanart, or fanfics. There are also so many ficfests and challenges out at the moment...I'm looking at summer and fall eagerly for new authors to squee about. Who knows? Might dabble in something myself.
Its a world full of opportunity (yes, now don't bash my head in for cliches)