My thoughts :
- In case of a full scale war, India's best interests is to keep it limited to conventional conflict. And pakistan's resources & manpower will run out much faster than India, simple due to the size difference between the nations. China will keep supplying money/fuel/arms, but there is no way it's gonna sent Chinese soldiers to fight pakistan's wars.
- In an event of a Sino -Indian war, there is every possibility that a conflict will be brought up on the western front to keep Indian forces/resources split up . But the vice-versa is very less likely because, if a full scale wall initiated will very likely be without china's approval (as any war is bad for china's economic interests in the region).
- Both countries wont be able to fire nukes at the other without taking atleast one hit themselves. From Indias POV, bombing lahore/karachi will also have the risk of the residual nuclear particles blowing over to India and causing huge contamination and death.
- Also Delhi, Mumbai, other major North cities & Bangalore are the most likely targets for a potential nuke attack. The defense installations in Vizag and the naval bases in Places like Kochi and military bases of dehradun are potential targets, but given pakistan will only have a small widow to hit maybe 4-5 targets before retaliation The causalities will be humongous.
- Also any unprovoked nuclear attack from pakistan will completely collapse whatever Hindu-muslim communal harmony we have. You are practically looking at Guj 2002, nationwide . Muslim dominated provinces Like Hyderabad, Kerala , Bengal etc will see some kind of resistance, but the overwhelming number of the Hindu population who are rioting will lead to maximum violence in those regions .
- Also the nuclear attack will severly damage the livability / agricultural prospects of the heavily populated Northern states (which will be the prime targets) , which will result in a colossal migration of people (bigger than the partition) towards the relatively less damaged far south and North east. That will exacerbate whatever inter-state divisions & disontent we have and can lead to a complete balkanisation of the country .
- Pakistan, I don't think will survive a nuclear war at all, owing to the smaller size. Also further rebuliding would purely depend on how far Iran & Afghanistan are read to take in refugees and weather the Gulf will bankroll rebuliding .
- Also unlike what some posters here think, largescale war followed by an ethnic cleansing / communal violence situation in India WILL NOT completely destroy foreign investment here. As long as the Christians (protestants/evangelicals mainly) are unaffected in the riots, the western nations will come back after some time. They did the same with germany and Japan after WW2. Economy and the quest for survival trumps all other humanitarian feelings. The Gulf may cut ties with India permanently , but given how unstable Saudi could become in the future, their economic might could greatly reduce by then.
All of this is from a purely academic "what if" perspective. Nuclear war of any kind will irreparably damage both countries. Even if India survives by its size, the sheer number of deaths , injuries and displaced population will be a global calamity on an unprecedented scale.
Like that scene in the titanic ,
once the ship sinks, the lifeboats that escaped prior, chose not to go back to look for survivors and thereby risk sinking their bots sink via overcrowding.
The same will play out in India, which will see a sort of Mad Max like dystopian situation , where nuke affected states turning into wastelands which will will be walled and the people (especially the poor) shut out by the surviving 'safe' states.
Patriotism / unity in the subcontinent will work only till the first nuke hits,
then its a rat race for survival. And given the sample that the partition Showed us, a post nuclear India/Pakistan will be far worse than any dystopian hell you've seen in the movies till now.
