If the US actually escalates to that kind of level, I am sure paki nukes will be the first target. The US on the face of it is kit going after Pak but the terrorists in it. Pakistan will have to decide if they would still want to be jn bed with the terrorist or save their nation from being sent to stone age, well split into 4. I think the Pakis will do what they did in 2001, a retreat by dumping the terrorists and living to fight another day.
I think with Obama eager to wind down ops in Astan, I would no be surprised if Pak compromises the Haqanis to give the US a sense of victory while actually nothing changes on the ground as someone else will become leader. What Pakis need is terrorists and they can make leaders out of anyone.