I don't think the Taliban are interested in attacking anyone else. Afghans broadly are happy to sit where they are and fight their customary enemies: other Afghans. After the heat Al-Qaida pulled on them last time, I would be surprised if the Taliban would let them operate substantially in Afghanistan again. Although that said, I think Al-Qaida has largely given up trying to kill Westerners: it's taken a look at ISIS and realised a better way forward is growing influence and power in the Islamic world.Or we let the country fight it out themselves and see what happens. So long as they don't start attacking other countries, which they will because they done it repeatedly throughout the last 3 decades, at which point we go in and murder everyone.
Besides, they're probably not going to be capable of attacking anyone else. After all, this is Afghanistan we're talking about. When we say Afghanistan is ungovernable, this includes by the Taliban. They only controlled about 70-80% of it back in their pre-2001 peak. They'll have a regime in Kabul, a few loyal areas, and everywhere else they'll have to hold by force. No-one likes puritanical regimes: opposition and resistance to them are guaranteed, and such regimes will only have authority where they have troops to make it happen.