An isolationist China would be great for the US in the long term. In the short term it would cause massive issues, as it takes time to ramp up production for things the US hasn't produced in decades. A lack of electronic components in particular would be a nightmare to deal with, as HK & China export 35% of the world's supply of components, and those components are needed to make more machines to produce them.

Not only are there very few factories available to ramp up supply, there isn't enough skilled workers to man them. China going full isolationist would make things a lot worse before they become better.

In 15 years after a complete collapse and social reorganization it would be a boom if the US survives. Walk into any store and find a product not made in china. It takes years to re industrialize. US has no domestic manufacturing capability and you don't go from nothing to something overnight. The machines to make the machines to reindustrialize are made in china. Case in point the US after 2 years still cannot make rated paper masks for the mask insanity nor ventilators, media complains about running out of oxygen regularly to deal with covid patients. All those things would be prime candidates yet no progress has been made in scaling the existing or establishing manufacture of these products. On top of that a majority of people are skill less and lazy and you would have to rebuild out of an economic down turn that is going to make the great depression look like a booming economy. Your talking about something that you wouldn't even see any results from for at least 5 years and likely the patient will be dead in a much shorter time frame.