Stop playing Call of Duty man!! the Afghan population will chew everything coming from Pakistan, flesh or metal doesn't matter! and will flood the plain terren of Pakistan via streets of Peshawar and Islamabad within days, Pakistan economically cannot sustain a war for more than a month inside Afghanistan nor PA has any experince of battle and equipment to fight in terrens like Afghanistan. The war will not be between ANA and PA it will be with whole Afghan nation against PA - Pakistani population are ducks infront of Afghans who are fighting from birth to death since 4 decades. Finally don't forget Pakistan's other enemies will not miss the chance to hit from left right top bottom
The above is my analysis for the current status of Afghanistan and Pakistan, but things will be different in 20 years from now ANSF will be a professional force with air defence and supriority and at that time Pakistan will think 10 times before going for any misadventure against Afghanistan just like it did in 60, 70s and 80s.