How many of them will actually go home when their visas expire?
Probably zero
There is no "probably" in that. Any sane person would choose to weather this storm in a safe haven. Going back to heavily infected countries is insane, and nobody can be expected to do that. It's not a matter of illegally earning a few dollars here and there, which is a choice; it's a matter of life and death, which is not really a choice unless a person is suicidal.