What would happen if China and Pakistan attack India?

SCENARIO 1 — China and India in a war →

Despite the rhetoric, the two Asian nations will not engage in an open war. Minor skirmishes and diplomatic grandstanding can be predicted but a war is highly unlikely. In fact the reports of military eyeball-to-eyeball confrontations are pretty common and perhaps under-reported under tacit understanding on both sides. The choreographed retreat on both sides is well-honed, since there has been no military death on the border for decades.
China has grouse regarding the Dalai Lama, while India alleges that NE rebels receive Chinese support. Such issues are fine.
A small brief incursion, like 1962, may also be difficult as India may quickly respond with Sukhoi squadrons in North East. Even the abysmal infrastructure on the Indian side may not warrant a quick incursion due to the dangers of quick escalation. Despite the mountain strike corps and M777, if and when they materialize, conventional advantage remains with China.

Also China has spent lot of capital in its attempt to integrate Tibet. Such a war may actually expose the soft-underbelly of China. Perhaps the world may be in for a surprise and will ponder at the wonders of Chinese integration (highly unlikely)
Despite public perceptions, there will be enough saner heads in India and China who admire the other nation. I for one am an admirer of the way China has pulled so many people so fast out of poverty (much more significant that some economic growth statistic)
Also other than the brief 1962 war, China and India have civilizational ties that span centuries. Buddhism, shared colonial tragedies, crucial members of global south and new members of the rising Asia are just a few commonalities.
Whether its UNSC reforms or NSG membership, China will oppose India. They will collaborate in WTO, climate change, global trade (both outside TPP) and to a lesser extent on IPR issues. Such convergence and divergence comes with the territory.
They will compete in certain areas even as they co-operate in others. I will say that this is a good model for it does not reduce the relationship to servility (Pak China — consider the Xinjiang troubles) or outright hostility (Pak-India or US-Russia)
The hostility may evaporate if we remove the border disputes. We currently have two very centralized governments with very powerful leaders (Jinping & Modi), who can push for an acceptable solution at the border. Can they push it ?

SCENARIO 2 — Pakistan India war || China forced to support its ally →

This will remain in the realm of higher possibilities
Consider it from Pakistan’s perspective. Apparently the core issue is “Kashmir” and relations cannot normalize till there is resolution of Kashmir as per Pakistan’s wishes. Contrast it with the patience and sagacity that China has displayed to resolve Hong Kong or Taiwan. When China’s stated policy itself is at loggerheads with Pakistani approach on similar issues, to expect China to militarily support Pakistan during hostilities would be insane.
Also assuming that China decides to support Pakistan, that escalation may force traditional allies of India to help India. This may lead to escalation of bilateral issue on a larger canvas and China may decide not to intervene to precisely avoid such escalation.

And we actually have a precedent. The 1971 war of Bangladesh liberation (kindly do not call it fall of Dhaka). During that time, the wounds of 1962 India-China skirmish were still fresh. But China preferred to sit out even as USA and Russia “meddled in” with exceptional gusto.

SCENARIO 3 — Hypothetical case of India under attack on two flanks, with rest of the world twiddling its thumbs nervously.

China alone is far more powerful. But India is far too bigger. To avoid nuclear war, we may have a small incursion and hold or an incursion and retreat to humiliate India. The second option seems credible as China has utilized it earlier in case of India (1962) and Vietnam (1979). Given India’s chronically pathetic infrastructure especially in North-East India, this is within the realm of possibilities. But ultimately it will not achieve more than give India a bloody nose. On the western flank, India and Pakistan will replay past stalemates. Even here the appetite to use nuclear weapons will be minimal and India’s Cold Start doctrine needs time to mature. Indian naval forces may blockade more effectively today, but international powers will force a cease-fire soon enough.

Pakistani generals will jump at the chance of such a scenario. Infact, it is precisely such a war that can be utilized to strengthen the grip of the politico-military feudal status quo in Pakistan.
But China? China may use a short war to divert attention from domestic issues (an economic hard landing or domestic protests) or to strengthen the hold of the CPC.
India can prepare for such an eventuality, but it will not indulge in attacking two nations at once. Remember that here is a nation that refrained from attacking despite deep provocations (Parliament attack, 26/11, Kargil). India’s strategic community is deeply defensive and because of a semblance of democracy the nation is more attuned to public reactions. India released convicted terrorists in exchange for kidnapped Indians (IC 814) and attempted to evacuate Indians in war zones (Yemen), where even “the West” refrained from intervening. Hence an Indian government will think hard and long if any option involves loss of Indian lives and that reduces the tendency to be a provocateur.

Parting Thoughts →

There cannot be a full scale war among the three. Even if one underestimates the collective sanity quotient of leaders, such a war will be short-lived and encompass mostly the border areas. If such a war escalates into any nation utilizing missiles, then the blame falls on the citizens of concerned nation, for having put in place such a vacuous misanthropic leadership.
Chances of India & Pakistan skirmishes remain high, since they already have fought a small war under the nuclear shadow. Chest-thumping aside, I doubt if any nation can deliver the other a knock-out punch.
But China may refrain from such misadventure. Also China may prefer to consolidate the South China Sea reefs as the 9-dash line is a more ambitious goal.

ClashSonic