I had it happen to a flight attendant. The simple solution is to stay on the plane and return to the US. But, nooooooo.
They made her deplane, took her to a secure area and kept her there until the airline paid an $8000 fine. It is not a quick process.
You need to understand the Chinese mentality. They are given a job to do. There is no deviation from the procedure. Thought and common sense will get them sent to the Mongolian border.
EC
But I think my suggestion about an emergency passport would have been possible.
Just sayin'...
BIL used to travel to China regularly for his job and he had a laminated card that he would use to point to to get to his hotel, airport etc. and he never varied by staying within the China system. One of his co-workers from another company (Disney) decided to go outside the system and got a Chinese version of Uber where he was taken to the countryside and robbed of everything. Passport, license, CC etc. I guess Disney was able to expedite his return because of their political weight.