There's not really a religions group that rules India, but if you meant which religious group will be dominant in the next 600 years, then the answer would be Hinduism. Hinduism is the most practiced religion in India, and considering the number of it's followers and the number of the followers of other religions, like Buddhism and Islam, as well as the fertility rate in each of them, Hinduism will remain the most practiced religion in India for the foreseeable future.