I think fiat will survive because the concept of physical cash can never be removed and i think we have to accept this fact but at the same time we will see crypto slowly dominating and increasing adoption so it would be like crypto having major share of global payments and remittance market in few years time so i think slowly we will reach to bigger avenues as far as crypto market is concerned.
I think in the distant future, humanity will gradually change from cash to electronic money because of its excellent solvency and security. Cryptocurrencies will be the main currency and the only currency that makes it easy to transact between people worldwide.
The reality is that the world is gradually restricting the use of cash, instead of online payment services. But cryptocurrencies are a completely different matter, to have the future as you mentioned, the world has to change comprehensively, and that's very unlikely,