Partition was politics, nothing to do with the military. India may have been destroyed and conquered in the past, but that has no relation to partition. You forget that India is a WW2 winner.
The 1971 war was a one-sided massacre. So that will simply be repeated again.
In fact it will be easier. In 1971, India fought West Pakistan, kept the PLA at bay, prepared to intercept the USN fleet and conquered East Pakistan, all at the same time. That's basically 4 fronts we had to take care of, which means our military resources had to be split between 4 regions. Today, in any Indo-Pak war, we only really have to worry about 1 front.
During that time, West Pakistan had access to nearly double the resources because they controlled East Pakistan. Now Pakistan is nowhere near capable of challenging India in any field.