I've gathered a little bit more information on his leaving. Its nothing against square-enix, or anything like that. He's only leaving so that he may work on games for other companies as well ^_^
Apon his leaving, he's opening up his own composition company that will do specialty services for various game companies who hire him.
So, basically, Mr.Uematsu may still do Final Fantasy games in the future, but rather then being part of square, he'd be part of his own company. ^_^
I think thats awesome personally, because I love Uematsu's compositions, and I would love to hear em in other companies games as well as square-enix's ^_^