I think it's likely that the first episode of the new season (which I believe will be showing up on the 22nd) will deal with Chef's departure. Maybe he'll get stuck in a closet, maybe he'll be replaced by a relative, or maybe they'll just kill him off (those bastards!). He hasn't been particularly prominent in the show lately so I don't think d is too likely.
a) Recast the part of Chef?
b) Kill off his character?
c) Use old clips of Chef for new shows?
or
d) Is South Park simply doomed?