It'd be a stupid decision because giving all of the former princely state of Jammu and Kashmir to one country in this conflict is stupid. Pakistan always wanted Kashmir, because it was one of the Muslim-majority areas in India. I don't know why you think that all of J&K going to India would somehow make everything all nice and happy, the only way to make India-Pakistan relations somehow better than OTL is by having Jammu and Kashmir being partitioned into Non-Muslim and Muslim parts (Non-Muslim areas go to India, Muslim areas go to Pakistan) as it was about to until the Maharaja overreacted and decided to accede to India.
Also, it is Jammu and Kashmir, not just "Kashmir", Kashmir is just some valley.