I can not agree more with you however that in case a solar explosion knocks out electricity or the regime changes to one of a nightmare, Bitcoin is going to be our last priority.
Exactly this. Yes, we had a time before the internet where the world functioned, but now that
everything requires the internet it would be impossible to go back to the old systems smoothly. If the global internet went down suddenly then everything would stop. Let's just look at food. Supermarkets wouldn't be able to sell anything since none of their registers would work. It wouldn't matter though cause nobody could pay since none of the card machines or ATMs would work either. So they would all get looted. But no more goods would arrive because supply chains would all be down and all transport routes and borders backed up for days, not to mention that most workers aren't going to work if they can't get paid. It would only take a few days before riots started over the rapidly dwindling food supply. And then consider things like electricity, gas, even clean water, all of which would face similar scenarios. Worrying about spending bitcoin in such a scenario is pointless - no one would be accepting it anyway. Things which would have value would be food, water, gas, weapons, and medicine. Bitcoin, fiat, and gold would be worthless, at least in the short term until either everyone figured out how to make everything work again or the internet came back online.
How do you make sure that Washington's mesh network is running the same chain Florida's is?
You either need a way to communicate with Florida to ensure you are indeed on the same chain (which could be via the mesh network if it were large enough), or you need both use an external reference point such as Blockstream Satellite.
In case they mine blocks separately and they collide at some point when the Internet is back up, is it not extremely insecure especially against double spending? If the internet shuts down and I have 1 Bitcoin in my wallet, can I not double spend it by spending it once in Florida and then moving to Washington and spending it a second time? If the two mesh networks do not communicate, there is no way Washington's has the information that my 1 Bitcoin have already been spent before.
Maybe. In such a case where either or both of the Washington or Florida mesh networks was running their own chain, then their hashpower would be reduced to that of whichever miners were on their mesh network, meaning incredibly long block times and an incredibly long time until the next difficulty adjustment, rendering bitcoin more-or-less useless. It would be far more viable for them to stay synced with the global network via satellite, and use mesh networks to send transactions through until they found someone with an internet connection (perhaps close to the Canadian border, for example) who can broadcast their transaction.
