Over the long term I’d bet brains are not zero sum — a brain drain really just means increased returns to education. Mobility means more people in the developing world will pursue higher education. Add to that increased flow of knowledge and capital to the developing world from migrants and concern over “brain drain” sounds very much like yet another disingenuous excuse for keeping the current system of inter-jurisdiction apartheid in place.
The International Migration of Knowledge Workers: When Is Brain Drain Beneficial? highlights another way brain drain benefits all. Abstract (emphasis added):
We consider the welfare effects of the emigration of workers who produce a public good (knowledge). We distinguish between the knowledge diversion and knowledge creation effects of such emigration, and show that the remaining residents of a country can gain from emigration, even when tastes for knowledge goods exhibit a kind of ‘home bias’. In contrast to existing models of beneficial brain drain (BBD), our results do not require agglomeration economies, education-related externalities, remittances, return migration, or an emigration “lottery”. Instead, they are driven purely by the public nature of knowledge goods, combined with differences in market size that induce greater knowledge creation by emigrants abroad than at home. BBD is even more likely in the presence of weak sending-country intellectual property rights (IPRs), or when source country IPR policy is endogenized.