is it possible to get your visa stamped on a new passport if you loose your documents in China?

If they lost passports in China and get new passports in China, they can get their visas on the new passports before their visas expires at the Exit-Entry Administrative Bureau of Public Security Bureau in China.

If they lost passports in China and get emergency travel documents to return to their countries, then they apply for new passport in their countries, they have to apply for a new visa in the China embassy if they want to come to China again.