See:
There Is No Escaping History. Fiat Currency Eventually Fails.
Notice that this is a critique of fiat money -- not a critique of state-issued money under a gold/silver or other standard. Fiat money is a rare occurrence in modern history. (We live in strange times!) As we can see, the examples found by the author are a small number of short periods here and there.
I have my own critique of gold/silver standards, but that's another issue.
It will fail and also crypto somehow will fail sometimes. Everything in not that perfect and would have some faults, so be wary of the things you want to say, because today, you are still using FIAT.
Yes, not just fiat will fail, but the crypto will fail too because everything cannot be always in the top position and sometimes it will fail and we don't know when the times are. But I think both crypto and fiat can give something benefits to us although it fails especially, we now still using fiat to purchase anything and we use crypto for the investment section.