Quick note that regular money works like this, although you might not realize this if you grew up in the USA since afaik it has never happened here. Governments re-issue all the money quite often. UK did it in 1971. India did it in 2016. It happened when the Euro was launched.
This is one of the main reasons why the US dollar has been the de facto reserve currency.
At least that was the state of affairs until 2008. Since then the system is more or less in decay, at least by standards which where held before.
Now, if your government is of the kind that can realistically announce over the weekend that cash is going to be worthless by Monday unless exchanged, then yeah. Then again, if you live in a place like that, you probably already know to keep your money in foreign currency and use the black market exchanges as needed.