Haven't you ever thought that the Pakistani arsenal exists purely as a bluff?
Do you guys really think Pakistan will use nukes on India when the Indian Army is running amok within Pakistan?
Where will the Pakistani armed forces and civilians hide if you so blatantly kill Indian civilians?
Here's what I think will happen in case India declares total war on Pakistan. Pakistani authorities will reveal locations of their nukes to the Americans for extraction. The location of the ones that are forward deployed, if any, will be given to the Indians so that we can take them out in missile strikes. This will be done in order to guarantee the existence of the Pakistani state, in other words, the Pakistani Army, in a post war period.
Or the alternate, Pakistan destroys one or two major Indian cities. India blows up a few Pakistani cities in retaliation, and then the IA takes over Pakistan and starts executing anything and everything to do with the Pakistani security establishment in revenge after pinning the Pakistani state with "crimes against humanity" and the whole world will support the purge and applaud it after it's done.
So good luck with your nukes.