I'm pretty sure the Pakistani general public had a lot to do with it. Musharraf was pretty unpopular by the end.
It may be that Pakistan is irretrievably lost at this point -- maybe not; but I think it's set to become a big mess.
If it really starts to dissolve, the most important thing will be to send in teams to secure the Pakistani nukes. I'd be willing to bet that the Pakistani gov't is even more alarmed than we are at the idea that Taliban might gain access.
The nukes will be brought out.
Doubtful given Pakistan's paranoia about India. They will not allow them off of their soil for fear that they will be vulnerable to India and that they will not get them back.