My biggest fear at the moment is if quantum computing becomes mainstream and hacking the network becomes ordinary.
Am sure then, bitcoin can become worthless as investors shall fear bitcoin.
You can abandon those fears. It will take many years before quantum computers become widely available. By that time bitcoin will be either long gone or upgraded to withstand quantum decryption. If we are to become rich thanks to it we will before quantum computing becomes a real thing. Don't forget that BTC is a software and as that it's upgradable.