I think the line is good in terms of finding future replacements. Bulaga, Lang and Newhouse are all young players that are only a few games away from attaining a starting job. The only question now is who would be their backups. As for the Center position, I wouldn't rush to find a replacement. Wells has done a good enough job and I doubt he would want a hefty contract. Even a mid-sized pay raise could keep him on the roster for several more years. Plus centers get better with age so it's crucial that we keep him till he peaks.
We already have 2 possible replacements for Driver in James Jones and Jordy Nelson. The question here is, which one of them will it be?