Would Indians have evolved to a Caucasian phenotype, had Europeans and their technology not arrived to interrupt natural selection?
No. Natural selection was a success. The thing is that the diseases killed 90+% of their people for 2 centuries, their elites and middle class murdered. The rest of the priviledged class assimilated and the peasant/slaves were sent to work on toxic mines for 4 centuries. What could happen to a population that suffer such changes?