This is the question of the people who not believing in cryptocurrency. We are now in the world of changes and digitalization.. We don;t know what will happen next.
Now developed countries are accepting bitcoin as their regular currency like China, Russia, Japan and now Australia. So it is possible that in the future bitcoin will be the global currency. In my country it is also not allowed but the people still invest and trade in bitcoin and if all the people start suing bitcoin for their payments of daily needs, no doubt that bitcoin will be the world global currency.