A good shooting war between those two would be something to see. Been a while since we had a good continental scale conflict.
A war between India and China would be horrendous. Pakistan would probably attack India too. We have a close relationship with India and a trade relationship with China, we would be paralyzed to take sides.
An escalation could start WW3.
It would be a disaster of Biblical proportions between two nuclear-armed combatants with enormous manpower.
The conflict could escalate into something that makes WW2 look like a picnic.