I think that's where you first get into "some other governments money may be less useless" as a first stage backup. Precious metals in direct ownership are really a hedge against all or most other governments money collapsing.
Until you reach a global societal collapse, having gold in your possession seems like a negative ROI and I wonder if, should that case happen, would precious metals again become the medium of exchange or something else (peoples' opinions have changed and a fist full of diamonds might not be as valuable to me as say fresh drinking water should such a thing happen). It would likely depend on the cause of global collapse and what people consider valuable (obviously, but it probably needs stated).
Precious metals seem to be a good medium of exchange historically only at a certain level of assumed societal infrastructure, similar to our fiat currencies. Cavemen and small tribes cared little of precious metals and would rather trade land, access rights, livestock, etc.