There's no way Cedar Fair selling Carowinds. The company has been making big investments to the park, and are even planning a resort hotel. Didn't Ouimet once say that the park "could become the Cedar Point of the South?" Now that would be a big task, but it does show that Ouimet really sees potential for Carowinds. So I don't think Cedar Fair would even consider selling the park.
Six Flags is currently focusing on building international locations in China and Dubai. I don't believe they'd want to buy another US park if that's the case.