"By non-fiat currencies, you mean what exactly? The only true non-fiat currencies that I can think of were all commodity monies, and as far as I know, none have actually 'failed' in any compariable sense. We still use gold, silver & copper. The non-monetary uses of these metals can over shadow their historic monetary uses, but they all still have a market/monetary value."
I think that we don't have much basis for further discussion. You use the term 'fiat currency' as a disparagement and therefore I assumed that you knew what the alternative to a non fiat currency is, one that is backed by gold or silver. Gold and silver are not the same as a currency backed by gold and silver.
And if non fiat currencies haven't failed, where are they today? And why doesn't their removal from circulation constitute failure?
And nowhere in the world today are gold, silver and copper used as currencies. Yes, they are a store of value, just as platinum, palladium, nickel or even coal, wood and bullets may be, but that does not make them a currency.