I guess he can always start a new user account with a different name and come back pretending to be someone else. Then we don't really lose anything.
Regarding residuals on this supposed R10 the story has been well known for a long time so most of the people who would have bought one, if they've done any research at all, should have taken that into account. Limited production of the car however should keep the effect down. It has that in it's favour.
Plus the balance of the car with the V8 is so good will always have a market: people willing to buy it or woodducks like people buying RS4's because someone told them to. The same effect could be said of a 911 to a 911 turbo I guess, if Audi price the big one far enough away it shouldn't cause huge problems.