It's easy to forget that the US, USSR, and some other countries conducted open air nuclear tests for many years before agreeing to stop in the early 1960s. Some of these tests involved single warheads with yields far larger than the combined nuclear arsenals of India and Pakistan. Here's a link to the test history. If you select the link covering US tests, you'll find a good discussion of the health effects of these tests.

I'm not trying to say that we have nothing to worry about from fallout should India and Pakistan fight a nuclear war. I'm trying to point out that open air tests by the US and USSR involved far more and larger weapons than India and Pakistan own and we somehow survived. Consider the US Operation Hardtack I series of tests that happened back in 1958. That series involved 35 warheads ranging from the low kiloton range up through 9.3 megatons. These tests happened from April through August of 1958. There were a total of 77 US nuclear tests that year.

That was nothing compared to the Soviet tests, especially those conducted in 1962. From August 1st through Christmas of that year, the Soviets conducted 77 atmospheric nuclear weapons tests with some warheads over 20 megatons in yield.

A nuclear war between India and Pakistan would be terrible beyond imagination but it wouldn't be the end of the world as we know it. Few people outside of the impact zones would be killed by the fallout. Unlike the contaimination released by a messy reactor like Chernobyl, the fission by-products from nuclear weapons tend to have a short half-life. Most of the radiation will have decayed to low levels within a few weeks.