What I believe the Taliban might do, as Afghans have done before, is move closer to the Pakistani border, east and south, where they have support in the Pashtun area (most of the Taliban are Pashtun). Along the Pakistani western border, lies the Pakistani Pashtuns. (I realize I'm probably stating something you already know)
If the Taliban fade into the population, especially where they have support, across the border as well as at home, they may be difficult to root out. Also, they could receive support from the Pakistan side. The border is porous and corruption is rampant. There is already a vibrant underground economy in that region of Pakistan. then it would be up to Musharref to try to work his side of the border, while not inciting civil war. It would be a tricky situation. The map, below, shows (in blue) the Pashtun dominated region between Afghanistan and Pakistan. the red line, in the middle, is the A/P border.
You raise excellent points concerning the ethnic tribes of the region. You’ve obviously studied this situation. The map you included depicts a disconcerting picture regarding the range of the Pashtun Tribe. I can only hope that despite the competing coalescing influences, such as ethnicity and religious faction, that a sense of nationalism will prevail. We are talking about a nation after all. There must be common bonds that cause Afghanis to think of themselves as Afghanis.
As to the Pakistani problem; let’s hope their president retains control. He seams intent on keeping us as an ally and may exert the pressure needed to keep things cool on the border. Though, it goes without saying, I wouldn’t trust anyone over there further than I could throw him.