Kyle, I agree with the number one response in the thread you sent.

He says: No one is bothering to upgrade now since the threat is in the far distance, as it gets closer (I have been watching… the number of entagled q-bits has risen very very slowly over decades. It may move faster, but it will not be 1-month from no where)

Chain upgrades are ususally planned over a year or more. Still when shit hits the fan, devs can do it in months or maybe even weeks. So there likely WILL be time.

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But even if someone DOES break SHA256 in a secret quantum lab, then uses this new secret ability to create a double spend attack on some chain. the world will know, and their bank accounts drained!

We can look at what happened with the ETH DAO attack. the developers fixed the problem, and the world agreed to just roll back time (like you are not supposed to do on a chain) and then ran time forward like the theft never happened.

It was VERY messy. But ETH is alive and well today. (well it forked the chain, but most money is now in the new fork.)

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So nothing about this doomsday scenerio rings true.