If that were to happen, it could be said that New Zealand had lost monetary sovereignty. To understand the challenges associated with a loss of monetary sovereignty, we only need to look at the countries at the periphery of the European Union during the Great Financial Crisis.
Today, I fear that those countries experimenting with adopting crypto-assets, such as Bitcoin, as legal tender might soon find themselves in an even worse situation. Bitcoin has no institution at its core that is charged with stepping in to secure the public interest in the event of a crisis.