The moment all the countries convert to crytocurrency would be the beginning of many amazing things to happen to the world and the financial sector, the process sending and receiving funds worldwide would become very fast and easy, it would lead to growth of businesses and make life easier for citizens of the world.
Yes, if all countries switch to the use of cryptocurrencies, surprising events will indeed begin, since the economies of all countries will immediately become out of balance and financial and general chaos will begin in the world. However, I assure you that this nonsense will never happen. But one state in the world will never switch to the use of cryptocurrency and will not give up its national money. Cryptocurrency will continue to go in a society together with national currencies of the states.