Love talking about rivers, especially that one in Egypt! 😁
Sorry, I have nothing to blow your perspectives out of the water. The currencies we use today are indeed merely concepts and only hold value while enough of us accept that they hold value. In the case of the failure of the grid, fiat could actually trump crypto as long as we keep its physical representative known as cash.
It's why we've never really been ready to take that step and put fiat into crypto. We're not keen on keeping it in the bank either, so to that big mortgage debt it goes, although there's still no guarantee even there that our property won't get removed from us. My grandmother knew that all too well. The war left her family homeless and stranded and we're talking about a middle class family in a first world country, here. They never did get to see the place they grew up again, because it ended up in another country and part of the USSR.
My aunt sent me a book for my daughters when they were younger. It was a history of Britain, showing how an area of the country would have looked thousands of years ago and how it would have changed as humans "progressed". This was a children's book and it showed a surprisingly stark reality of how far things regressed when the Roman Empire fell. It cycled back several hundred years. Then of course it moved on into modern times and what we have today, more built up than ever.