Considering how well they are playing without him, I think it is a smart move to get the surgery now.
When healthy, he is still one of the best big men in the league, and I think with some tweaking of the roster this summer, he can be the key piece to turn that roster from a 6-8 seed into a top 3 or 4 team in the East, and competing for a title. They need to make the right moves this summer, but the potential is there.