The USA could keep functioning at full bore for 50 years without any external inputs into the US economy? You're dreaming. How much of the shit you buy at Walmart, or anywhere else is actually "Made in USA"? The first thing you'd have going on is emptying of store shelves as people rush to stock up on everything, you'd have a ballooning black market, massive inflation and empty store shelves with scenes like the 1970's Soviet Union economic collapse.
Meanwhile, the rest of the world would see an immediate production surplus (the USA imports more than it exports), meaning price cuts for materials and goods. This would lead to increased consumer consumption growth in the rest of the world, which would offset the lost markets fairly quickly compared to what the shortages in the USA would do. Consumers will snap up bargains due to surpluses much quicker than you can engineer an entire supply chain to compensate for shortages in basic products.
The one "good" thing that would happen is the sudden devaluation of the US dollar to be worth about a penny. This would be great for the Feds. The US debt would be render worthless overnight, and new money could be printed. And it would be good for employers. Since $15 "minumum wage" would now be literally 15 cents. This would help in creating the sweatshop-like conditions needed to resupply the USA with basic products to replace those lost from imports. But a lot of the culture would be annihilated. Say goodbye to car culture, because few people will afford cars and you'll have to go for public transport. Say goodbye to American AAA games and Hollywood blockbusters, because those rely on foreign markets for much of their profits. They just won't be as viable as investments as they are now.
As for the rest of the world, the complete disappearance of the USA might hurt for a few years, but basically the world economy would realign around new markets. We would lose a customer, but we also lose a competitor. There are countries which have a trade deficit with the USA, but there are other countries which have a trade surplus with the USA. Logically, we'd just start trading with each other instead. Certainly in very short order the 7 billion of the rest of us would economically outpace the 300 million isolates in their Trump Fortress.