Hot take
If the commodity value of the metal that resides within fiat currency is higher than it's face value you have an arbitrage opportunity--albeit an illegal one with significant PoW currently running net negative ROI. Perhaps even the most soundest of money if acquired at a deflating fiat value.
It's certainly possible future generations will desire modern coins for their commodity value despite their relatively inferior metal contents simply because the metal commodity is higher in value than face value. Gold and silver valuations will price out the sheep too stubborn to see leaving lesser and lesser metals as the only option.
