No one can really tell what will happen in the future. Bitcoin has scalability issues and if its widely used, there would be some problems with network congestion. I guess bitcoin will remain a good store of value just like gold because of its scarcity its value will always increase together with its mining difficulty.

There will be a new crypto that will represent or be widely used in online transactions.

FIAT on the other hand will always be there since every monetary unit represents a country's exchange for goods and services and there are also some remote areas that has no access to new technologies like crypto.