China should be civilized and not ruin the lives of hundreds of millions of people because of geopolitics. India breaking up would be Yugoslavia breaking up times 10000.
India is already very decentralized with states formed with ethnic, language lines. State governments also have a lot of autonomy that operate almost like mini-governments. I don't think it will be like Yugoslavia. It might be more like breakup of the Soviet Union.
Great powers pursue policies that reduces threats and also boost their own influence. India as it is now is a huge threat for China. Yes, China is utilizing Pakistan to keep India off balance. But I don't think this will be viable long term. Sooner or later India will get powerful and super ambitious. They are already supporting Chinese adversaries like Tibetan Seperatists, Philippines and even Taiwan. Its obvious if they get powerful in the future, they will stop at nothing to cause problems for China. Sooner or later China will have to focus on India.