Cases in Nevada are growing very quickly now. And if the cases don't stop to rise state authorities will have to lock down Las Vegas again.
If that was attributed to the opening of casino, then there is a reason for the casino to be close again, but if not, I doubt the government would close the casinos as they are generating funds for taxes.
It doesn't need to be attributed to the opening of casino, once the cases is rising, that means the area is at high risk of infection, so the government's initiative is to limit the businesses which requires a mass gathering for them to profit, and one of that is a casino business.
If there are other ways then maybe the government would consider as we all know Las Vegas casinos are contributing millions of taxes to the government and that's vital for the economy to survive.