Major Fiat currencies cannot "fail"...
Because they are the only way to pay taxes and stay out of jail...
So every Fiat Currency has a fundamental value >> Tax Base...
(We are not talking about Banana Republics here).
This USD "fails" nonsense is floated by people...
Who have never filed a Tax Return or held a meaningful job in society.
Seeing most government officials with bloated paid and mostly do nothing but process paper. I don't necessary agree those who filed tax return held a meaningful job.
Now that I think about it, many jobs in the west are pretty meaningless since most exists for the sole reason to comply with government rules and regulation (accountant, lawyer, government employee and etc etc..) Do bankers in its current form serve society in a meaningful way?
Major currency can fail. History is repeated with major empire debasing their currency before the final collapse. The final blow to the coffin may not be the implosion of the economic. But if a small band of barbarian can take down Rome (in the case of US, a small group of people take down an entire building in the world financial center or a disaster causing the state to paralysis, or a few companies causing the world finance system to melt down or a few teenagers causing school/city to panic), this implies the government/company/society is infested with incompetent and greedy people who do nothing but take pay check.
I welcome anyone to offer counter argument.