Ah, yes. The age old question. My answer:
No. Not in the slightest.
While yes, people leave the game, tons of new players JOIN the game too! The numbers seem lower mostly due to the fact that many have stated before: school.
I can't really say much else without repeating what others have said too much. Red and Cruel Fears are pretty spot on.
Honestly, the same thing happened to IT except it went down because of hackers, and then the source was released, and many people branched out and created their own, active private servers. I'm not saying the FH will end, but it seems like it's heading that way. I hope it doesn't though, this community just seems so unified because it's just one server.