KH and FF can't be compared in that respect. FF is unique in that the stories, characters, and locations are all different. That's why it's so marketable. They have a few things that can make it an FF, but, in the end, it's not a sequeled game. Not like KH is.
And KH is almost eight years old, we can't forget that. So, I'm not saying it'll die out within the next few years- of course it won't.
But within the next ten to fifteen years, it will be obsolete, for the simple fact that they can't make that many games that deal within the same universe, with the same cast of characters.
They can do remakes, and manga, and novels, and perhaps an anime all they want. But that doesn't mean that the series won't eventually die, for all that I'd rather it live on forever, considering how obsessed I am with it.
And no, you can't have read this entire forum, because that would be a major waste of time. You're saying that you've read this entire thread, which makes much more sense. However, even if you have read it, you'd also notice that a lot of us would buy the collectors edition if it came out, that we have legitimate reason for believing that it will eventually die (because not even good things can last forever), and that it doesn't matter what any of us believe, because it's all up to SE and Nomura.