If Lester was resigned, the rotation is still good. Lester, Lackey, De la Rosa, veteran, Owens/Ranaudo/Webster is a pretty solid group.
Tazawa is still around long term, Uehara will probably get a qualifying offer and come back for the $15 million. The rest of the bullpen is a crapshoot, but it always is.
Pedroia, Ortiz, Victorino, Napoli are aging, but they haven't exactly missed big chunks of time over their careers. Add a bat like Hanley , Tulo or Stanton and the offensive dynamic really changes. There has to be a good bat in Xander, Betts, Bradley, WMB, it just might take a few more months to find it.
I see plenty of potential, and there is plenty of money to get there. Losing Lester would be the real problem.