I think Buchholz' option should be picked up, but the FO cannot depend on him to be the ace, or to give the team a full season. They have to acquire a bona fide #1 for next season.
As far as Pedroia and Papi go, saying that you can't count on them for anything next year is a bit of an exaggeration. I understand that they are both getting older. I understand that the way Pedroia plays, coupled with him being older, puts him at risk for injury. He is still a very productive player, though, and he's far from being the problem of this team. Pedroia is the last player I would ever bet against.
I would be more concerned with Ortiz for next season than I am about Pedroia, due to the simple fact that he will be 40. Even so, I wouldn't count him out either. And like it or not, he will be back due to his vesting option.
The key is to always have a viable back up plan. The youngest, healthiest, best player can get injured or hit a break wall. You have to plan for such.
IMO, your idea would make more sense if the team were indeed going into full rebuild mode. I don't see that happening and I don't see the need for that happening.