they may also have to replace China as the source of cheap labor for the West.

Besides the climate catastrophe -- which I'm with you in hoping humanity finds a way to mitigate -- there's also the problem of building India into a modern advanced industrial economy that can replace China. China's industrialization is rightly seen by the rest of the world as a kind of miracle, made possible (though western countries hate to admit it) by the fact of its being a Marxist-Leninist state. Specifically, land reform, political unity, the government's ability to mobilize the masses, and a theoretical framework which understands the role of capitalism in the context of Chinese and world history have been the cornerstones of China's economic success. The west likes to boast about how capitalist investment "raised" China to what it is today, but the fact is that no other government could have done with that investment what China did. Certainly Modi's government does not have the power, ability, or necessary base among the people to achieve what Mao, Deng, and Xi have done.