If no one wants to buy the old ETH, then it won't be profitable to mine, so no one will mine it. Without mining there is no security (as far as the old PoW chai

If no one wants to buy the old ETH, then it won't be profitable to mine, so no one will mine it. Without mining there is no security (as far as the old PoW chain is concerned.) Kind of like how Ethereum Classic (ETC) is subject to 51% attacks every other week and requires multiple days' worth of confirmations after deposit to any exchange.