I think there are other countries who could take them as well. I think Brazil and Argentina might be able to accommodate some. I would think all the US allies in the world could come up with a plan to deal with this. It shouldn't be solely the US's problem.
They should not leave. Some of their ancestors have been in South Africa since 1650. Things may be bad now.
But it's quite possible they'll improve in 20 years from now.