The Soviets wanted a vassal state. The US does not.
We left Afghanistan alone after the Soviets left. All Omar had to do was not get involved with Osama bin Laden and Al-Qaeda. We were no 'bull in a china shop'. Afghanistan was hardly anything worthwhile for US. But now the region is clear on one thing, china shop or not, the US will bulldoze everything in our path when we put the will to task.
When we leave, the Taliban can have Afghanistan and the Muslims will cheer the usual 'graveyard of empires' nonsense. But behind closed doors, everyone knows that what happened was a lesson hard taught to the region. First it was Afghanistan, then it was Iraq, and we broke no sweat in both. We also learned our lesson, that from now on, it is futile to engage in nation building, especially in the ME. We will not leave the ME as we have interests there, but those who are hostile to US and are stateless will not find allies like Al-Qaeda did find with Afghanistan because of what we did to the Taliban. The next generation of the Taliban -- am willing to bet -- is not the same as the time of Mullah Omar and Osama bin Laden. They will not be interested in spreading their version of Islam but content to rule Afghanistan.
Regarding IS, while it is a threat to states, the US and Europe would be the last on its list of targets, except maybe for the isolated incidences of terrorism, so what this means is that if IS continues to be a threat, it will be up to the regional powers to treat any state that sponsors IS the same way that the US treated Afghanistan. This also means we maybe looking at yrs of internal strife if not outright civil wars in the Muslim states.