Overrunning the Pakistani state

Following up on Evan's Baitullah Mehsud post, I'd like to see someone game out a realistic scenario in which the Taliban "overruns" the Pakistani state. Foreign Policy estimates that Mehsud has 16,000 fighters (and that's one of the higher estimate I've seen). The Pakistani army has 800,000 soldiers.

Obviously the numbers don't tell the whole story. There's a nexus between the Taliban and parts of the army; some soldiers would be reluctant to fight the Taliban. And the army's heavy-handed tactics create millions of refugees and lead to widespread resentment.

But it's still hard to imagine a scenario in which a few thousand Taliban -- not terribly popular with many Pakistanis, either -- overrun the entire state.