Wow that's big news, is understandable if he wants to spend more time with is family. I am pretty sure he'll be back but this time as a head coach, and probably the Knicks head coach. He did a very good job as Rockets assistant coach, he helped Yao a lot.
His resignation is legitimate, family is important. Don't the Rockets still have another big man assistant coach similar to Ewing? If they do, then Yao is still in pretty good shape as for the learning.