I left China a few months ago after cancelling my WP, but my residence permit is still valid for the next six months (stamped). My ex employer wanted to cancel the residence permit as well, but I was in hurry to leave China, so we didn't do anything about it.
Now, I'm not sure what would be the validity of my RP since I've left mainland China. Can I fly in and out showing the same RP at Chinese immigration? Will I be flagged at the airport and get in trouble doing so?
When your work permit was cancelled, your residence permit was also cancelled, at least in the Immigration database. If an Immigration officer scanned your passport's ID page, your status would come up on their screen, and they'd know you're not a resident anymore. The officer will start looking for a new vvisa, won't find one (but will find your residence permit and cancel it), and ask you where your visa is.
At which point you'll be sent away. No penalties, usually, unless you try to argue and make a nuisance of yourself.
Just get a new visa.
