I doubt that this will be a career ending injury for Yao, but I do think it will affect his mobility going forward. With his build and statue though, I don't see that as a large problem, unless it leads to future injuries. He just needs to stay big to block shots (no jumping required).
Stability in joints is a good thing, especially for big bodied individuals. What worries me is his age, and need for a huge multi-year deal to consider moving from Houston. Sacramento also is a smaller market, and the Chinese government will have something to say about where Yao can play I imagine. Overall, it would be a good move if it didn't take more than a 4 year deal to get a healthy Yao to Sacramento, but there's too many variables to do more than wish and speculate.