He has yet to see any drop in his "skill" ratings, with only a marginal drop in his relevant "raw" ratings. High makeup and high training should help stave off decline.
He'll lose some skill rating points, but not enough to make him worthless by end of contract, and perhaps not even enough to make him overpaid at $7.3M. An injury would wipe him out pretty quick, but with 90 health, that's less of a concern.
If you are really that concerned about it, I'd suggest a team/mutual option for the final season, but realistically I'd expect that to be more useful for a 4th season, because even if he isn't demanding it, that guy is good enough that someone will offer it to him.