All 2nd-hand information, but hopefully of interest.
David Kilkullen's book, 'The Accidental Guerrilla', covers some of the reasons why people take up arms.
In line with what has been said above, Kilkullen claims most guerrilla's aren't interested in fighting outside their borders (be they clan or, possibly, country). On that basis, the Taliban 'only' wanted to rid Afghanistan of foreigners. So while they likely will be a deadly menace to their countrymen and women, they may not be a threat to any other country. Hope this plays out ... but have to feel for the terrors they will impose on Afghan citizens.
In the "The Looming Tower" (Lawrence Wright) claimed the 1990's version of the Taliban were not enamoured with Al-Qaeda and their activities. There was potential for serious conflict between the Taliban and Al-Qaeda until 'the West' tried to pressure them. Being resistant to things western, the Taliban backed off from harassing Al-Qaeda. That did not turn out well for many hundreds of thousands of people, nor for the Taliban.
If the Taliban have learnt that lesson, they may not be too keen to harbour terrorists ('freedom fighters'*) in Afghanistan.
* aside from Al-Qaeda, their were many other groups in Afghanistan including those seeking to overthrow governments e.g. Mubarak in Egypt. It would seem few, if any, shared Bin Laden's hatred of things Western - particularly the USA - to the extent they would have taken their 'war' outside of their particular target.
How (if?) the Taliban handle Daesh (ISIS) may be a different game again.