Were airworthiness certificates revoked for B737 Max?
The grounding of the 737max is a Prohibition of Operation, not a revocation of Type Certificate. This is done by each jurisdiction around the world. China suspended flights two days before the FAA did.

Technically, if you could find a country that never prohibited its flight, the Max could still be used there. Repositioning flights of grounded aircraft, as to a storage location, are authorized on a case by case basis.