The CAFE requirements are spread over the entire lineup of the company. I can't see the Corvette being that much of a hinderance to GM's CAFE number, at least not nearly as much as the trucks. If they continue to sell 15-30k cars a year, that is less than 1/3 of the Camaro sales, so if a car was going to take the hit, it should be a Camaro, not the flagship of the company.
And with the Camaro going to a smaller platform, a turbo4 getting mid20's/mid30's MPG should be easy.