India is a democratic government. China is governed by a comunist regime. The two do not make for mutually condusive relationships.
There are a lot of ifs, maybes and speculation. Russia could reserge. China's economy could collapse. Brazil could find a substantial source of oil that rivals the middle east and become a major world power, etc, etc ad infinitim. Anything can happen in the long distance future. Why because there are too many variables which could have long term ramifications further down the road.
If 3 years ago we could not even predict the global economic recession that would occur in 2008 and 2009, what makes us think we can predict long term historical events 20, 50 or 100 years out? If you want an interesting read about the unpredictability of predicting future events read Asimov's foundation series.
For me, it is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring.Dr. Carl Sagan