I think the one example of this actually happening was in London, and the billionaires who did leave did not actually contribute anything to the local economy: as many of the workers they employed as possible were migrants brought in or outsourced and they kept skimming profits off the top to hoard. The businesses they ran continued operating as normal even if some got sold off.

EDIT: and they’ve been movng back because the place they fled to was Dubai lmfao