Much like how the invention aeroplanes did not eliminate water transports like ships, vessels etc. It just give shipping industry a different focus.

It is safe to look at cryptos this way. With the existence of crypto, you expect a slow increase of circulation. When at a certain point, say 10% of world are using crypto as a medium of exchange, that will be the time fiat would slowly take a back seat.

But fiat is not expected to disappear altogether. It will probably play a different role in the financial world. It may even probably become the alternative form of wealth measurement.

It is really hard to say since we are technically into the 5th industrial revolution already. With the influence of Artificial Intelligence and variius sophiscated technology... the economy may even be partly run by AIs.

Who knows...