Don't think thats useful in terms of currency exchange. In order for a crypto currency to be transferred it has to be committed to the public ledger. If you are cut off from the rest of the internet you can never have a successful transfer. I don't think people in Russia and Ukraine can wait years to convert cypto to local currency. What could happen is a fork of that cryptocurrency could be created in Russia with a completely different set of transactions. It could never rejoin the main chain otherwise that full transaction log would be lost.