Regarding quantum computers and if they able to break Bitcoin cryptography, do you still think bitcoin would be worth any thing?
... And once quantum computers can break elliptic curve multiplication, ...
Not only quantum computers, it is also possible, that they will find a way to calculate secp256k1 curve faster. Some are trying to find a way:
Calculating Satoshi's coins
https://bitcointalk.org/index.php?topic=5347791.msg57395610#msg57395610Think of it as sunken ships with these mined coins as their cargo.
And we want to salve these ships and recover the coins.