They must still take an in person class, and risk having their visa revoked if not. That's just not about being in the US, you can't be a foreign student at a US university without a visa. You'd have to take academic leave until you can have it reapproved.

They can take more than usual, but even if the school's not open 100% they cannot take "an entirely online course load". Some schools have already announced all instruction will be online and a lot more are probably going to.