Sutil won’t get a drive at Ferrari, his was decent at Force India, but his results didn’t merit him a chance at a top team. Buemi and Alguersuari are good, but I can’t really see Ferrari signing either of them. If Massa went early, then a solid and experienced driver would be the best choice (i.e. Barrichello or Heidfeld), but I can’t see Ferrari hiring them either.
If Ferrari got rid of Massa, then I think they’d have to take a chance on either Fisichella or Bianchi. They both know the team very well and would have the full support of the team. When Heidfeld replaced Kubica at Renault last year, the team never fully supported Heidfeld, possibly due to the lack of relationship before hand. So hiring a free agent or a driver from another team would be a real risk to take, as Ferrari may not even fully back them, the replacement will just be made to play second fiddle to Alonso.
Personally I think keeping Massa for the whole season is the best move, he knows the car, even if he hates it. If Massa just regularly scores points from on, that would have to do, a replacement would likely not score points at all. If Massa really struggles to score points this season, then Ferrari should give Fisichella a try. If Massa can at least score points often, then Ferrari should keep him.