If the U.S. is crushed economically the rest of the world is dead whether we respond militarily or not. It would be all we could do to supply ourselves with food and exports of food (and other critical supplies) would stop dead in its tracks.
If we have to go into survival mode the rest of the world is on its own without the huge surpluses we have been selling and giving away for decades.
We would hurt but we would survive. How would Russia and China do?
China has been buying-up USA farmland.