I wouldn’t worry about this too much. Brain drain, despite the name, is not really a zero-sum game. The people who move rarely lose all contact with the host country. They gain invaluable experience, know-how, and contacts that some of them eventually bring back to the host country.

I know of more than one example where someone has been “brain-drained” to the states, who has subsequently moved back to start a successful business. Sometimes leveraging gained contacts directly, sometimes leveraging the newfound experience and knowledge.

Whether this works out this way depends on how open the world (or at least the respective countries between each other) is when it comes to movement of people, money, and trade.