although massa has been crap he is still the most likely for next year, if they pay him off they take money out of their budget in the resources restrictment agreement which would hurt alonso if they leave perez for another year at sauber he comes in with a bit more experience, they can see how he does throughout a (hopefully) uninterrupted season.
Paul di resta is a mercedes nurtured driver, and so is more likely to make a move to Macca sometime after button or hamilton leave…
alonso wouldnt want Hamilton at ferrari, seeing as hamilton beat him in his first season (albeit on race wins).
Webber has a drive in the best car, and would be mad to switch.
anther who could take the ferrari seat is sutil, out of a drive next year, takes sponsorship with him, which would help pay off massa.
hamilton is most likely to stay with Macca until they come out with a few more dogged cars.