Perhaps one day with the current bitcoin advances, bitcoin digital currencies will be an international currency for all countries, and make it easier for every human to make transactions between countries when going to another country.
if it happens in the future it will certainly affect the paper money that exists around the world, whereas we know when the banknotes have a lot of history and symbolize the diversity of a country with other countries.
if that happens, surely the government will not remain silent on the matter, there will be an agreement between state governments to immediately close the bitcoin network to the world.
what will you do if you have a lot of bitcoin.
Unfortunately, in that case there is nothing you will be able to do about it as you may not even see an exchange to make use of and you could as well just be bag holding your bitcoin hoping that one day, you may as well just get to spend it again.
Nevertheless, no need worrying about situations like this as I do not see in any way where the whole government all over the world will deliberately gang up against bitcoin to make it nonexistent. Most especially, there is nothing to hold against it even if it becomes a threat to fiat and worst that can happen is strict regulation which still does not affect anything much.