I think it is very unlikely that we will see a worldwide crypto currency issued by a central bank since that will require a government so powerful that it can impose his will above the will of the other countries and while the U.S is very powerful is not that powerful.
I think cryptocurrency will not be able to master the major currencies in the future, as long as the government has a fiat then it will be difficult for cryptocurrency to be the main currency in the future
It would be really impossible for bitcoin to surpass fiat because fiat currency is being regulated and controlled by the government which we all know that they are the most powerful in terms of implementing rules on a certain country thats why bitcoin would not possible to be a main currency.
Yes indeed bitcoin can not surpass fiat, but bitcoin could be an alternative to fiat in future payments. I believe bitcoin will grow so much that using it as an alternative of bitcoin. But it will not make money disappear because I'm sure the money will continue to be used. Money is not just a transaction but as the strength of the economy of a country.