I'm sure if the FIA made it an advantage to run Turbo Diesel engines you might see Audi in the WRC. But Audi don't want to lose so they either wouldn't be there at all or they'd put so much money in that they would almost surely be guaranteed success. But of course Audi's image doesn't quite lend itself to cars being dirty and so on I predict Audi staying on the track until Peugeot gets close enough for them to get scared and then they will go "Ummmm errr we won lots we have nothing to prove now" and leave rather than having to play second fiddle to a "lesser" brand like Peugeot.

If there's one thing that's as sure as the sun coming up in the morning and setting in the evening (unless you live very far north or south of course) it is that Audi will come into a series and dominate and when their advantage disappears they will quickly go off to another series and do the same thing there