Absolute nonsense. The monetary commodity begins as just another commodity (per Mises’s regression theorem). It is possible for multiple monies to co-circulate or for money to be different from region to region. Throughout most of Western history, gold and silver have co-circulated. If the gold supply becomes so restricted by comparison to the silver supply and is unable to keep up with the demand for hand-to-hand coinage at realistic valuations, then people will switch down to silver until gold supply catches up or population goes down or both or maybe the switch would be permanent. Yes, gold holders would lose some money in such a change-over as gold would fall to its exclusively non-monetary commodity value but that uncertainty is present in every part of life, there is nothing government can do to change it, not through fiat or any other way. It would be up to individuals to choose their own portfolios in such a way as to protect themselves against such events.
The opposite could happen, as well. For example, if some new technology permitted cost-effective gold harvesting from the ocean - where the vast majority of the gold in the world exists - there could be a new gold rush. In such a case, people might want to switch out of gold into platinum or silver.
Clayton -