There is at least one totally "offline" backup of blockchain? I know that it can be a little paranoid yet, but anyone ever did an offline backup of blockchain in case of a kind of geomagnetic storm? Imagine if all clients of the world lost the data. I know the entire world will be a mess, but the Bitcoin could keep safe.

Maybe it isn't necessary (or even possible) to keep an offline copy of blockchain, but it could be in a hard disk isolated in a special hardware.

Is it possible? Am I thinking something wrong? Thanks.
This question in Skeptics SE asks "Will the Sun's magnetic activity disrupt electronics on Earth?"

As I understand it, the disruption has a limited geographical area of effect, and protection for a device can be achieved by simply disconnecting the power and network cables to disconnect it from long-distance grids (which amplify the effect). 

I'm sure there would be some offline backups available even if every PC that was plugged in was fried. I would assume servers in data centres would mostly have adequate protection already. For the vast majority of people with an interest in Bitcoin, the other effects that might come with widespread power and network outages would almost certainly be a bigger worry than any issues with bitcoin.

All that said, I recommend keeping multiple backups of your wallet in a variety of locations. Maybe you should keep a reasonable amount of cash handy in case of emergency too, if you're worried about geomagnetic storms...