I think this is good for him salary wise
I agree he will get plenty of other opportunities (sponsorship contracts) outside of basketball too. He might not be Chinese but he is still hella popular over there, meaning financial incentive to move to China was too big to pass on, along of course with getting to be a starter again and playing meaningful minutes.
What's the chances that he can get back playing in the NBA?
If you ask me chances he plays again in the NBA are very slim. I will give you, for example, Jimmer Fredette, another undersized point guard, he had his Linsanity moments but in college, played like 7-8 years in the NBA and then moved to China. He tried to make a comeback this year, signing with the Suns but only played in 6 games. Made the Warriors roster for this year's summer league but didn't get any interest from other teams. He was avg. over 37pts in China.

Once you are out of the league, comebacks are tough. So yeah, at his age 31, Lin probably played his last game in the NBA.