What might happen in Zimbabwe:
1- The internet may be cut off at some point, which will stop the buying and selling process throughout the country
2 - The party responsible for Bitcoin may withdraw all its currencies from Zimbabwe and thus become a country without a currency that can neither import nor export
Cutting off the Internet is like commiting economic suicide, you can't have a developed economy without the Internet. This can only happen in the most shithole of dictatorships, like North Korea.
What do you mean "the party responsible for Bitcoin"? Bitcoin is decentralized, each hodler is responsible for their own coins. I can't imagine a scenario where 100% of the people decide to move from the country and take their coins with them. This doesn't happen with fiat, so why should this happen with Bitcoin?