Nice point - though let me give you a small example - what happens to the vast dollar reserves that each country hold to - and uses for trade? what do countries do with that much worthless paper and how would someone quantify it or get compensated or get replacements for it? what would they use to buy stuff if suddenly they realize that they have nil reserves?
Or, what would happen to the long term or short term trade deals that countries and corporations have entered into that is solely based on the exchange of dollars as currency?