They do not have to sell him this year. They do not need the money - and - that transfer money does not run away as he will be as expensive or even more the next season. And de Bruyne does not really seem to force leaving this season. They do not have a replacement for him - and it will be difficult to get one as good as he is.
If he wants to leave they will sell to Bayern, too, if de Bruyne wants to go there. There is no problems between the two clubs.
The German player that did the big advertisings for Volkswagen in the last year was not a Wolfsburg player but Thomas Müller. Volkswagen needed him for their World Cup advertisings. The Bayern players are contracted not to do private car advertisings - so it was an agreement between the two clubs and Audi and Volkswagen, too.