it would create huge hardship to the people of South Asia and destabilize the entire region and possibly beyond. I hope that stupidity does not become this strong that such war becomes reality, but one never can know. It would be tragic.
It depends if you talk about conventional or nuclear war. Nuclear war would have a worldwide economic impact. But the economic costs of a conventional conflict should stay quite limited to both countries. The Pakistani economy would suffer more and take years to recover while Indian economy should escape it rather untouched. I don't think that even a full-scale conventional war would have a significant effect on the world economy.
At present both country have maintained nuclear balance as well as deterrence. Although India has upper hand in conventional military power and economic strength as per GDP. If both country will wage war, it will affect not only their economy but also whole region too. Modern war is very expensive and developing country like India & Pakistan can not effort the economic cost of military war. Both country are heavily depended on others for their weapon supply. Of course, arms suppliers economy will be strengthen during India- Pak war.
Pakistan going through a political crisis may find it difficult to withstand the economic fallout of war. The mess created by the hybrid government in Pakistan is too bad for the Pakistani establishment to even contemplate a war scenario. India has its own compulsion to push for development. According to India, the sheer scale of economics will create conditions for Pakistan to exercise restraint.
Should rationality fail, the outcome of the war will be catastrophic for Pakistan and damaging for India