I’m pretty sure that all crypto (hence the name) relies on encryption to run the block chain. Quantum computers will be able to easily break encryption. So how will this not be used to immediately control the blockchain?
The rest of the global economy depends on encryption; cryptocurrency is a tiny portion of that. (In that context, worrying about cryptocurrencies after a core cryptographic algorithm is made totally vulnerable feels like worrying about whether your flower bed will be damaged by the giant tornado that's going to destroy your house.)
Everything will need to migrate to post-quantum cryptography. But this doesn't need to happen today, and more research is still needed.
Quantum computing doesn't break encryption itself; it breaks the discrete log problem (DLP), which is admittedly often used to generate encryption keys.
Besides, we seem to be decades away from building quantum computers that can run DLP breaking algorithm. Despite all the reported progress over the last decade, they have yet to factor any number beyond 21 with a general quantum number factoring algorithm like Shor's.
The future Mars-coin by Elon is not based on encryption, but centralized database and tickets sold on Mars. You can trade only Mars-futures on Terra, but they are 30 minute futures. Destroy that.
Everything will need to migrate to post-quantum cryptography. But this doesn't need to happen today, and more research is still needed.