Earlier in the season it made no sense to play Tony. It makes sense to play him now, however. It would give him some reps and help him shake the rust off. Even quality veterans are rusty after not having played a while. The sole reason to play him is to get him ready in case Dak is injured in the playoffs and Tony needs to come in and lead the team. Yes, it's try playing Tony risks getting him injured, but if he were injured it would be way better to have that happen in a game that doesn't count so that we can get Sanchez ready to back up Dak. It risks ruining his trade value of he's injured, but his trade value isn't that high anyway as an older, oft-injured quarterback. It's likely we release him anyway instead of trading him.
Play him. Give him one last hurrah for the team he carried so long, and get him ready for the playoffs.