It's a question of acceptance.  The only thing fiat has going for it is wide acceptance.  We each decide what we want to accept in exchange for the goods and services that we provide.  Today, most people let the bankers and politicians make that decision for them.  The bankers and politicians are very grateful for that, but in the future I think most people are going to prefer a medium of exchange that has a fixed, finite, inelastic total supply that isn't centrally controlled and manipulated by bankers, politicians, or anyone else.

Precious metals were the best alternative before Bitcoin came along, but now the market has to choose between not just fiat and precious metals, but cryptocurrencies as well.  When it comes to precious metals vs cryptocurrencies they each have their own pros and cons which I think will lead to both of them increasingly being used as money for the foreseeable future.  Fiat currencies, on the other hand, offer tremendous advantages to some, but tremendous disadvantages to everyone else, which will make them unsustainable over the long term.