It could be a limited war that doesn't wreck much of the planet. Maybe back-channel diplomacy keeps the war limited to Southeast Asia and the war ends with Pakistan being dismembered by India and the USSR.
Or perhaps the Pakistanis do something a bit more provocative on their own, leading to a Soviet invasion with the U.S. staying out (albeit no doubt providing lots of arms and money to the Pakistanis to bleed the Soviets as much as possible) since, after all, the Pakistanis brought this on themselves and a nuclear war would be too much of a risk.
Reagan will be remembered in the short run as the man whose recklessness led to the loss of a major U.S. ally in Asia, although in the long run, people might think an end to the Partition was a good thing.
(Of course, the obvious response is that Reagan didn't INTEND to reunite India.)
This is a possibility. Although this would be a huge drain on Soviet resources, the loss of life would be staggering.
I doubt this would work out well for India. Not sure how India is better for having poor, war ravaged territory added on.
Mmm, hell, I could see Reagan being very upset about the way his policy worked out. Perhaps even resigning after an speech where he takes full responsibility?