I always wondered what would happen if a country using the Euro right now decided to back out and go back to its own currency. Wouldn't exactly the same thing

I always wondered what would happen if a country using the Euro right now decided to back out and go back to its own currency. Wouldn't exactly the same thing as the above proposal occur? ie. Everyone in the country is suddenly paid the new currency, exclusive usage is mandated so by law and taxes require payment in the new currency. There would be fewer Euros needed for internal Fiat so those Euros could be invested and thus the switch should make everyone in those nations that little bit richer right?