In regards to the Taleban, I'm marginally more optimistic than you guys. I don't think the Taleban have an interest in conquering and keeping all of Pakistan. To explain this, I will need to provide a bit of background.
Pakistan is not a homogenous country. There are several ethnic groups in the country. One of them is that of the Pashtunes, who live in the northwest of the country, bordering Afghanistan. The Pakistani-Afghani border was artificially created by the British and went straight through Pashto territory. "Afghani" is in fact the Persian word for "Pashto".
I know you are going to ask what all this has to do with the Taleban. The Taleban are Pashtunes -or Afghans- by definition. Their ideology is a mix of Pashto nationalism and the branch of Wahhabit Islam that is taught in Deoband, a Qur'an school (or madrasa) in India where many exiled Pashtunes sought spiritual refuge following the ongoing war in Afghanistan in the eighties and nineties. To the best of my knowledge, creating a worldwide Muslim theocracy was never on the Taleban's agenda, they only wanted to create a new Afghanistan according to their ideology. Since they are nevertheless Islamist extremists, their rule provided a safe haven for foreign Muslims, particularly al Qaeda which also follows the Deobandi ideology, to breed and grow.
So what I believe the Taleban are trying to do is to somehow establish a foothold in the Pashto territories in Pakistan, where they believe to be safer than in Afghanistan. The Pakistani government obviously does not want that, so they are fighting them. I'm sure that someone in that group will try to get their hands on Pakistan's nuclear arms, but nobody will allow that to happen. I can see India occupying Pakistan's nuclear facilities before the terrorists get their paws on them, since they would be the most threatened country if Pakistan should fall apart, which I wouldn't rule out. Even if the Taleban don't want to control all of Pakistan, others will. There is a pretty dangerous homegrown Islamist/terrorist movement in the country, and I think they are a bigger threat than the Taleban. They are the guys who killed Benazir Bhutto, after all. If you must have a buzzword, they have ties to al Qaeda.
To sum it up, I can see Pakistan falling apart, but I can neither see the Taleban themselves taking control of the entire country, nor can I see terrorists getting those bombs.