I'm a fan of Community. Like the show. Anyways…
Article explaining how the show may handle Chevy Chase leaving.
http://www.avclub.com/articles/community-has-a-plan-for-its-final-chevy-chase-pro,89323/
Be warned as there are "kinda" spoilers on the season finale in the article and in the quote spoiler tagged below
! > Or, maybe something less definitive than that, as reportedly the crew already rather wisely shot the season finale out of sequence, ensuring Chase would still be there through the end. And as to what might happen beyond that, should Community pull off the miracle of getting a fifth season? Hey, don't worry, because the fourth season ends in "a cliffhanger that leaves the fate of several characters up in the air—including Pierce," making it that much easier to write him off should the show manage to return. And if it doesn't, well, what do Community fans love more than being left to dangle anxiously, wondering forever about the fate of things?
! Ignoring the fact that a fifth season is unlikely, c'mon. This is community college. Jeff should graduate by then. Where could they take it from there that doesn't feel unnaturally dragged out?
! Yeah, yeah "6 seasons and a movie". Four is plenty in my book.