When you fly in China , your license belongs to the company. So , if you leave you have to get a release letter. It`s up to the company to give it or not.
As far as I know if you comply with your contract to the end , they will provide you but....don`t take it as assumed.
By the way. I just talked with a friend of mine whose husband flies for Tianjin airlines and it is pretty much the same topper described.
5 days out of home and 1,2 off.