No, India really can't manage a full fledged war against Pakistan-China combine unless nukes get involved. Heck, India can't even 'win' in an offensive war against Pakistan. The defensive nature of Pakistan's war capabilities are more than adequate to repulse India and that fact is known to all in the world.
The big question here is: How far will China go for Pakistan and how far will Pakistan go for China? If that question is settled and if nukes are factored in, then I believe the combine Pakistan-China can grab a lot of territory from India. Big IFs, yes, but the possibilities, if not probabilities are there.