To the same places other rich ex-US citizens have gone.
Switzerland has been a favorite destination for the past 60 years; my daughter is moving there in May, most likely never to return and she’s anything but rich.
One of the things most don’t realize is that this emigration, (out flow) isn’t limited to the wealthy because if a person is smart enough to figure out how to work grants, loans, and scholarships, that person can live on foriegn study grants as a perpetual student for 20 years. I learned about that from a co-worker who’s daughter did so, traveling the world, for 20 years; she finally married a Scottish professor.