I agree with shpadoinkleman. Everything they did in the last 15 years happened while South Park was on the air, so it proofs the show isn't keeping them away from anything. So why stop if they still have fun and many fans around the world enjoy the episodes? I am looking forward to the Book of Mormon movie as much as Ia am looking forward to every new South Park episode :).

And (I guess Will can relate to this very good ;) ) I would feel like suddenly out of work when the show stops. I have been running a big South Park fanpage for over 10 years now and it's an important part of my life. No other project they might work on in the future could replace South Park for me. Never, no matter how good it might be.