I'm not learned enough to answer question 1... but I don't think the fiat system is fully resistant against catastrophic black swan events either.
As for question 2 - it depends on which blockchain and which use case. Blockchain does not need to replace Visa in it's entirety in order to add value.
I'm not taking a side on the fiat vs. crypto debate. I'm inquiring purely about the technical aspects of the blockchain.
That being said, with non-blockchain data storage, one could create backups, so that if all the live running data stores were somehow destroyed, one could recover to some previous point in history with the redundant copies.
I'm trying to understand whether this, or any other sort of failure recovery, is possible with blockchain technology.
I see. I think it's possible. If there's a catastrophic event that nukes everything, it's certainly possible to restore from a prior state... or even multiple prior states. You would effectively get a fork or multiple forks and then the ones that folks decide to use en massed would become the dominant chain. It's happened already when there have been disagreements in how to scale protocols, or even in the case of a pseudo-catastrophic event like the DAO hack on ethereum.
As for question 2 - it depends on which blockchain and which use case. Blockchain does not need to replace Visa in it's entirety in order to add value.