He never imagined he would return like this: laid off, in debt and pursued by a sickness racing around the globe. Home was a small village ringed by coconut palms and paddy fields on India’s southwestern coast. His father, pushed by poverty, had been the first to leave for the Persian Gulf in search of work. Later Ramakrishnan, 47, and his four brothers all made the same voyage. “Ever since I was young, I wanted to go,” Ramakrishnan said. “I used to tell my father, ‘Just take me with you to the gulf.’ ” The family was part of a vast migration from South Asia to countries flush with wealth but short on labor. The migrants worked to raise gleaming cities in the desert, and built the schools, hospitals and power plants that helped transform collections of villages and port towns into modern Arab countries. Now, one of the largest migration corridors in the world is flowing in reverse. The coronavirus pandemic and crashing oil prices have led to mass layoffs in gulf states, leaving foreign workers vulnerable and in some cases destitute. Out of money and fearing the virus, hundreds of thousands have returned home. With a vaccine still months away and the number of coronavirus cases rising around the world, there is little prospect that anything will return to normal any time soon for the world’s 164 million migrant workers who cross borders. About one-third of them come from South Asia, and India is the single largest source of such migrant labor in the world.