You’re making some confusion. Dieselgate was a new chapter in the private war between Porsche and Piech families to control VW Group (that exists since the 60’s, with VW privatization), but it didn’t change the overall VW centered business. No matter who is chosen to lead, the group flag is always VW.
Btw, Muller was a VW group guy all his life; previous to the Porsche job, he had been Audi and VW top exec; Potsch is a former VW CEO.