Sure, but presumably the miners leaving will still want to do something profitable with their mining equipment. I'd expect to see the hashrate increase for other PoW coins. Unless there's some reason for that not to happen.
There is a market for coins with the same hashing algorithm, specifically to attract miners that can't do anything on the bitcoin blockchain.
They are all useless and don't have exchange rates to justify the electricity cost. You can launch a new one given the assumption that this is many miner's first halving.
The price to yield to electrical cost market is pretty efficient, rarely a long lasting advantage there.
