What if WW3 destroys under sea internet cables? China/europe miners could have their own chain and Americas miners would have their own chain. What would happen when they connect back? Could 6 confirmation transactions be reversed?
I think you are right. Bitcoin (and any other crypto) will fork so many ways because the regional nodes won't be able to communicate with nodes in other continents or states. (At least we will have some BTC on each fork....)
Even if the electricity stays on - decentralization will be its downfall - until order is restored again.
It may however be a good store of value if it is in paper wallet or hardware wallet form. You can verify the balance and hand over an IOU based on the BTC value.
Rather than spending the actual bitcoins exchanges could cold store the BTC and provide BTC based tokens in the meanwhile that are either exchange based or on a localized network of nodes.
A bit like how gold, silver and assets were used to back cash. There could be an introduction of BTC backed IOU's by institutions that hold the BTC (I know this sort of defeats the purpose of BTC but it is a work around and financial institutions will continue to work out ways to get their hands on your assets) . The only issue would be that Governments don't take kindly to anything that may resemble cash.