1948 UN Resolution for Kashmir was never workable from its origins. If Punjab & Bengal divided in 1947 on the basis of Muslim majority, why not Kashmir? Pakistan should demand a referendum only in Srinagar Valley where about 8 million people (95% of the population) are Muslim.
Pakistan should amend the constitution to integrate Kashmir as a 5th Province in km² :
Gilgit Baltistan-72,000 km² + AJK-12,000 km² + Srinagar valley-16,000 km² = about 100,000 km² in total.