The big follow through would be stuff like we’re doing now: building schools, helping the government get established, basic foreign aid type stuff. Some like to call it nation building, the important part is that it’s not just walking away without even so much as a “thanks”. We fought a proxy war in Afghanistan for the better part of a decade and when it ended we left almost as quickly as the Soviets, not only did it leave a power vacuum it turned a lot of people who were our friends into our enemies. Made it pretty clear we were just using them to irritate Russia, didn’t really care about the Afghani people. We made the place ripe for take over by people like the Taliban and then had the audacity to be shocked when it happened.
I suspect that the "security environment" in post-Soviet Afghanistan would have forced a military mission on the US fairly early-on. As I said, the US public would probably not have supported such action.
It's the same problem we faced in post-Saddam Iraq. You only need several dozen motivated trouble-makers with a few infantry weapons & some explosives and they can keep a neighborhood in an uproar.