Here in my country fiat money is good with digital wallet so i think our country are so different base in your post actually all has worth so i don't believe in fiat money that failed because if the things exist of course it has worth like bitcoin it run because users,traders and investors use this an investing tools so that's why it continue to grow
I think fiat money value differ in every state since economic stability and government protocol differs as well including cultural values which is also another factor that affects economy. In my country fiat money does not always fails but like cryptocurrency it does increases and sometimes decreases too. However, the flactuation rate is not as high as bitcoin.