If quantum computers advance to a certain level and Satoshi Nakamoto’s private key is cracked, will the Bitcoin economy collapse?
Nothing will happen to Bitcoin Cash. BCH gets spent all the time. It is a peer-to-peer electronic cash system. The network will migrate to quantum-resistant addresses long before quantum cracking becomes an actual threat. As for Satoshi coins, if he is alive, they are his to spend however he likes. If a quantum computer cracks them first, they simply become a massive bounty that re-enters the circulating economy. For BTC, the protocol itself won’t collapse. However, the resulting panic might drive BTC maximalists to take stupid actions that could lead to a collapse.