Frankly, I do not think that South Park really fears getting sued by anyone, and if they do, I am sure they have the revenues to deal with that...
But I just dont believe that anyone is going to sue South Park...because if they do, that will of course, call more and more attention to themselves, and how they were made fun of...people who never watched South Park before, will tune in, the episode will probably be rerun and rerun, and the person or entity doing the suing will find themselves more and more in the news, and more and more the butt of jokes...most celebrities or groups that are being made fun of, will just weather through the ridicule, and they know, that the very next episode of South Park will be skewing someone else, and someone else will be made fun of..
That's because you're smart. :~D I don't think they do either.
The Scientology episode this season proved that. Didn't it end with Stan saying, "Sue me" to the Scientologists. And the John Doe and Jane Doe credits ... ROFLOL. Such a shame the season is already over.