Fiat is not indispensable, hello. Did you forget that human societies used to primarily have metallism-based economies before central banks managed to entrap the entire world in a system of debt slavery?
Sure, and that gold standard failed. Fiat (with a money supply that can be discretionarily managed, and allows for monetary policy) is indispensable to a modern economy.
This is a dumb question. The Fed can endlessly print as many dollars as it wants. They could print $20 trillion tomorrow. See? Just think about how much gold would be required to back that $20 trillion! Clearly gold is stupid. Right?