So every year of Fletcher's career was as bad as the one he had last year, and no player who ever had a bad year ever played decently again. And Checkwa's issues have mostly been due to injuries, and you are telling me that no player who has ever had injury problems ever was healthy again.
Here's the deal. Players do get better and healthier and players as groups CAN play better as groups than they can as individual parts. And just as its likely that the individual talent at CB won't be as good without Revis, it might end up being better at DE, DT, LB and S.
Remember I'm not saying we shouldn't go out and try and improve at CB, OG, etc We should. But we should also remember that much of that "youngest team" to win a suprbowl is coming back. All isn't lost because one CB isn't going to be there