A Communist country's economy is a an artificial construct that cannot grind to a halt.
If you no longer have foreign contracts (US) to keep your plants in production, you can no longer provide jobs for your state employees.
If you can not provide jobs for your state workers, they can no longer purchase food to feed their families.
Without their primary income coming from the US, they can not purchase the necessary fuels to run their energy needs or fuel their economy.
China is the largest importer of oil in the world, shut down their ability to purchase and their suppliers and China is dead in the water on all fronts.