It's probably going to be a loss for them because those who may wish to do business with cryptocurrencies, or think of starting a startup or something that involves cryptocurrencies, they will probably move to a country that allows them to do that without any problems, such as the UAE, which is very friendly when it comes to crypto and people from other countries moving there to run their businesses because they know it's going to grow their economy because of the money they can generate from these businesses, and it will also grow their technological infrastructure as well in the long run.
I don't think citizens will emigrate from Greece and bear the costs of traveling and living in another country just to manage their crypto assets, unless they are wealthy and own millions of dollars in crypto assets. Greece doesn't prohibit cryptocurrencies, it simply doesn't have regulatory laws.
However, The Greek government is the big loser in the end because it will lose the taxes generated by these cryptocurrencies, as well as the significant investments that could come from abroad.