Regarding quantum computers and if they able to break Bitcoin cryptography, do you still think bitcoin would be worth any thing?
We will fork to a quantum resistant algorithm long before quantum computers pose a serious threat. And once quantum computers can break elliptic curve multiplication, then pretty much the entire internet will be at risk. If bitcoin isn't worth anything, then neither will fiat.
The danger with quantum computers concerns only those abandoned P2PK addresses most of which are doomed to be emptied maliciously in the future.
It concerns all coins in addresses with exposed public keys, which includes many reused addresses.