Whew! I just went through my warranty papers, and the seat warmers aren't covered by the extended warranty. But, my standard warranty doesn't run out for another year or 3,000 miles.
My dealer has been pretty darned good, I think I'll try to get her to replace all the heating elements. If she wants to replace the entire seats, and the new ones don't match (Cedar/Grey), then I'll replace the covers myself.