Very much like they diminished the content of precious metal in the coins they also happened to mint...
And the side effect was the free market valued the coins at it's metal content, so the soldiers then demanded a larger amount of 40% coins instead of a smaller amount of 90% coins to afford their daily expenses. Hence, you are just bringing up the fact that the metals are immune to government manipulation since their actions actually accomplished nothing by tampering with them. Rome didn't collapse because of sound money, they collapsed from completely unrelated reasons and then tried to tamper with sound money and discovered it was pointless
But all kings and emperors which came after the Romans were doing basically the same. In fact, the Greeks had been doing exactly that even before the Roman Empire. So there is no reason to think that the history would not be repeated again if we are to return to gold or silver coins. The only way to solve this problem is to issue paper bitcoins and provide a mechanism that would allow independent control (e.g. through the blockchain) over which paper bitcoins correspond physical ones, thereby making online transactions with these bitcoins impossible...
I think it is a by far better idea than what you suggest