Yes. The mechanism is that American kids stopped learning useful things like STEM skills. I remember when I went to college in the early 00s, every single person in my physics class was either an immigrant, child of an immigrant, or Jewish. Now we have a shortage in engineering skills that has to be filled by H1Bs, and a population that all gets service jobs and consumes disproportionately because of an overvalued reserve currency. If that currency ever stops being overvalued, we're fucked.

The U.S. is 4% of the world population. Back when the world population was 2B people and the developed world population was about 400M and the U.S. was 130M of that and the only market whose capital stock hadn't been totally destroyed by WW2, we were crucial to the world economy. But now the world population is 8B, the developed world population is 6B, and the U.S. is 330M of that. In terms of raw size of consumer markets, the world can ignore the U.S. The tricky part is the dependence on U.S. software and financial companies for significant parts of the global information infrastructure, but there's already a strong movement to that.

A nitpick here, but "visa" gets tossed around a lot. A visa is a document which allows you to request permission to enter a country for some purpose. To work in a country you need a work and/or residency permit. Even in the US, there are situations where you can work with a an expired visa, provided your other immigration documents are current. But if you leave, you need a new one. Similarly UK citizens can still work in some European countries without a visa, because there is no requirement for them to enter with one (but the officer at the border might still refuse entry).

Since the word used was "returning", that would mean that they go back to where they came from, where they are citizens.