"Unless they have red flagged your name following information from the PSB, you can leave without hindrance."
Red-flagging your name is a distinct possibility.How do you know your employer won't do so once he discovers that you've broken your contract by departing without first having had the decency to cancel it with him?
Having Chinese documents taken from you when you exit the country as per above,in line with this thread's heading,wouldn't scare the kind of person who would act in such a dishonest way.And most probably he wouldn't be needing them in the future anyway.
Note that Turnoi's request for information from this thread's originator has fallen on deaf ears up to now, certainly not the first time such a thing has happened on this board.Most likely the originator feels he can solve his problem,if any,without any additional advice.