It seems look like impossible things for me, but if that all happen I think they will create their own national cryptocurrency itself. Maybe they will create some coin that have same system like USDT or the other stable coin.
OK, if all the governments that accept the crypto and they have their own coin of each country, the fluctuation of the coin value will be no longer, they will stabilize like the common currency of each nation. But this is unlikely to happen, as the use of cryptography has been difficult.