I'd think it would be more Iraq 2003 than Afghanistan 2001. I don't see our SOF guys being able to pull off what they did in Afghanistan due to the lack of friendly forces available, especially if INdia were involved or even the specter of Indian involvement. With that off the table you're looking at invading the country. Marines coming over the beach and maybe from the west, Army from the west, SOF hitting the nukes and their infrastructure, maybe taking out some leadership or key scientists, and air power killing everything. The mountainous terrain and locals would prevent a speedy conquest of PK. I'd envision the PK mil putting up a fight before going the Fedayeen route like Iraq did in 2003. At that point you have guerillas to contend with, irregulars, hit-and-run stuff.
How do you deal with that? Were I in charge I'd introduce India into the equation once the nukes were dealt with (eliminated or marginalized) and allow India to bear the burden in the east. I would NOT allow PK to remain as a soverign nation, proxy, district, city-state, or performing arts center. I would invade to destroy the country, eliminate it, Islamabad Delenda Est. If you're the Pakistani's do you fight America or India? The response may be one of geography, but emotionally they'd go with the devil they know (America) rather than a sworn enemy, especially if we announce that Afghanistan will own everything west of the Indus.
Nation building....We're already into the "No chance in hell of this happening, Free, no matter how right you may be." so let's continue. Treat it like Germany and Japan under the Marshall Plan and make our aid contingent upon security. Right now, I'd tell the Afghans to GFY: live in shit, starve, watch your children die, and see ya', wouldn't want to be ya'. Send the message to the entire planet that America will be your ally, but if you start killing Americans we go home. That is the policy I'd extend to the Newly Conquered Area Formely Known as Pakistan. When I was done I'd go before the UN and remind everyone what we shell out to the UN, to NATO, and to any other junior League of Nations wannabes out there and then I'd ask them, "Does anyone want Next? Does anyone want to put their quarters on my pool table?"
There would be howls of protest and righteous indignation, but I guarantee you that no one would take the bait. Wait a decade or two, beef up their military (China and Russia), but an immediate response? No.
We would take horrendous casualties if we invaded PK. SOF, Army and Marine infantry, and the AF would be reminded of the value of CASR....but we could do it.
We just never will. I think once we wrap up Afghanistan we're going to be gun shy about war, especially commiting troops. Drones and remote bombing are the way of the future because we are soft and risk adverse, not because they are better, but because they are more polticially acceptable.