I realized I don't think I asked the question as I wanted. In this scenario the country doesn't switch to the coin, the currency is just BTC, built upon BTC, and will continue to rely only on BTC, not some foreign currency like USD or Euro. What I'm thinking is just a new country. Like the idea of Esperanto land.
it depends on "when" you are talking about this hypothetical scenario.
right now and probably for another decade bitcoin is volatile so if a country were to use bitcoin its economy would get wrecked as price shoots up and drops with bubbles and crashes. the "value" of the country's currency should remain moderately stable otherwise nobody can do anything.