Bitcoin can answer to a crack, that was done before with a rollerback, but some attack would be bad for the business could be a complete CAOS for a while.
It's not a crack what I'm talking about, it's physically tricking the network or something like that. I doubt that it's going to work but in theory, it sounds plausible. That's why I suggested, instead of using Quantum computers to make normal computers, hashes, obsolete, why not make it more powerful using that technology? It's far ahead into the future but it's better than destroying things.
With the amount of transactions bitcoin currently has >300k/day, a rollback is almost impossible. Planning a rollback and getting everyone to agree with it would take some time, and what would you do with the >300-2000k transactions that were confirmed before the rollback?
That's the thing, you can't. Maybe if we are talking about theories, certainly, we can but it's all a theory unless you have enough power to hack everything and Bitcoin would turn inside out and all those things that you sold for BTC, wouldn't be worth it anymore. That's only true if it happens, which is impossible to do.
Maybe, if there would be a HUGE theft that would be noticed immediately, but that would have to be REALLY huge. I cant imagine such a thing happening anymore.
We will never know unless something happens unexpectedly, knowing the will of other people just to destroy other peoples hard work, it's just the reality anymore. What we need to worry about is what hackers do with their knowledge.