About miners going out of business is something we can't talk about presently, I don't know if POW will be erased entirely from ethereum blockchain, I've seen coins that has both POW and POS functioning on same network, all we can do is wait and see.
According to what ethereum platform are trying to do, it will use another algorithm entirely, there will be no more PoW but rather PoS for ethereum mining. We need to talk about this now and presently, because there is possibility that PoS will be the modern way of coin minimg.