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.
and we should look around to see similar examples in other cryptos.
For instance bitcoin's halving is going to happen no matter how many miners is going to quit mining btc after it.
Ethereum should think of users, not miners imo