It's definitely possible for a certain cryptocurrency to attain this level of adoption. Is it guaranteed though? Definitely not. Who knows? The sort of "global currency" probably wouldn't even be decentralized, probably something like PayPal. Also, who knows? If it we're to be a decentralized cryptocurrency, it might not even be bitcoin. It's just pretty early to say for sure.
so much stupidity in this forum
no there will never be a single currency worldwide, controlled by a single instance, and even if it cant be imposed on the world without violence, people will always try to resist.
the us dollar that is currency globally accepted only has such wide spread because american military soldiers, are still listening on US dollar funded propaganda, and the elites around the gulf that sell the major oil for shipment globally, accept the us dollar for oil.