I would make the following assertions (supporting arguments can be culled from many many past posts):
1. A safe haven is the most important element for the survival of any such movement. There would probably be many scattered Taliban if there was no Pakistan next door, but they would not be a well organized alternative in the face of overwhelmingly superior military force without such a sanctuary AND (perhaps even more important) without the assurance that "one day the infidels will leave and the ISI will still be here, so fence sitters should think about the future and remember certain lamp posts in Kabul".
2. There would be no NATO occupation if there was no Pakistan next door, since the international jihadi network was founded and grew in Pakistan (with very generous CIA support), not in Afghanistan....Afghanistan became a base later and remained dependent on help from Pakistan..how many Jihadis landed at Kabul airport to join duty and how many landed (and at a reduced rate, still land) at Pakistani airports? The mismanaged and misguided occupation of Afghanistan is ONLY justifiable as a very indirect and badly thought out way of making Pakistan change direction. Invading Pakistan not being a real option in any case, the question is if THIS indirect approach was handled correctly or not.
3. This is also not to argue that NATO could not have effed it up without any help from ISI...just that it would have taken more incompetence than they usually exhibit. With average/usual incompetence factored in, this occupation could still have forced a compromise on almost all Afghan power-brokers, leaving small bands of true believers to gradually outlive their welcome in faraway valleys.
4. This is all "could have been". By now, it may be too late. If we are lucky, China will handle the "forced modernization" of Afghanistan in the next iteration of history's nasty cycle. By "lucky", i mean if we dont have any nuclear bombs go off. I am optimistic on that count, but who can guarantee such an outcome?