All I've heard was that after this season, Matt and Trey have the opportunity to renew their contract to do a 16th season and so on. Since they were nominated for a Tony Award for "The Book of Mormon", maybe they'll clear up any South Park questions there. (The Tony Awards are June 12th, by the way.)
I will admit though, some moments in the episode made me question whether or not it was ending... I guess the best and only thing we can really do right now is wait and see.