The problem is that you're dealing on the one hand with a democracy (and the Indian people have no real affection for the Chinese), and on the other, the stereotypical committee of pointy-haired bosses repeating each other's drivel as if it were Gospel Truth.
A China-India alliance would show very different dynamics; you're going to have to account for them in future books (either explain WHY the normal political dynamics of China and India were completely overturned, or make it happen WITHIN those dynamics, and then try to figure out what the ensuing results would be--and keeping these unlikely bedfellows in bed with each other would probably involve some very unnatural contortions that neither would be overly happy about).
And the other issue still stands: China would have to be extremely desperate to engage on an operation of this magnitude, and would probably be facing the prospect of economic collapse just to embark on it. Chinese culture--particularly at the top of the decision-making pyramid--is just about the most consensus-driven, risk-averse culture out there.
Having many relatives that lived through the times, and having talked to them ... talk of a Hitler-Stalin alliance before it was actually announced would have absolutely PEGGED the unlikely meter. It was absolutely unexpected and not something anyone was concerned about at the time. Yet, as we have stated, it happened.
Also, I do not believe we can draw too many conclusions about the Red Chinese. They are experts at distraction and deception ... it's in their blood.
But agan, the novel is fictional and as such you might call these things literary license ... or not. It's up to you.
Thanks for the feedback.
Regards.