No they don't.
There are many many fiat currencies currently in existence, and those haven't failed.
Your statement boils down to "Fiat currencies that have failed have a 100% failure rate", which is content-free.
On the same basis:
"Democracies have a 100% failure rate"
"Countries beginning with M have a 100% failure rate"
Regretfully yes they do eventually fail.
https://bitcointalksearch.org/topic/m.7692168
All fiats die..all fiats die.....btw all fiats die!!!
Dollar is in decline and will eventually disappear . It may well take a few decades for that. I suspect cryptos whether bitcoin or Government/ financial Institution created will replace all fiats over time as they are just BETTER in so many ways and less expensive to use.
"Every 30-40 years the Reigning Monetary System Fails and has to be retooled"
http://georgewashington2.blogspot.com/2011/08/average-life-expectancy-for-fiat.html
According to a study of 775 fiat currencies by DollarDaze.org, there is no historical precedence for a fiat currency that has succeeded in holding its value. Twenty percent failed through hyperinflation, 21% were destroyed by war, 12% destroyed by independence, 24% were monetarily reformed, and 23% are still in circulation approaching one of the other outcomes.
The average life expectancy for a fiat currency is 27 years,
If you read through the thread it was suggested that the British pound was the longest lasting and still in existence but the answer to that was ..It is not the same as it was and has been monetarily reformed on the gold standard/ off the gold standard/ decimilization so its not the same fiat even though it has the same name.