First, I wouldn't read too much into Bolden's performance against the Bills. The Pats had to patch together the OL on the fly, and the run blocking seemed to generally take a hit; also, Buffalo's front seems pretty decent at stopping the run. Even Ridley did not have the greatest day running the ball. If the other RB's on the roster can keep the defenses honest enough that Brady can run the play action, the team will survive the loss of Ridley.
Mayo will be much tougher to replace. However, last season it was the combination of losing 3 defensive starters in the front 7 that killed them, not just Mayo. I can see the defense adapting over time; both Collins and Chris Jones seem to be improving as the season goes on. Wilfork also seems to be getting better, even if he's not close to the Wilfork of old. Like to see Hightower step up as well; he's looked OK this season, and by some accounts he was close to returning Sunday. But there is no longer any margin of safety from further injuries, and it seems wildly optimistic to just assume that the team will suffer no more major injuries going forward.