Even putting aside the fact there are reportedly still American citizens stuck in the country, along with tens of thousands of Afghans who desperately wanted to leave but were unable to make it onto the last flights out of HKIA, there are going to be long-term effects of the Taliban takeover. Among them: Captured data, waves of refugees, the weapons on the global market, and emboldened radical Islam.
As with our experience in Vietnam, Afghanistan will shape our politics and diplomacy long after the last servicemember withdrew.
Captured data. Given the rapid collapse of Afghan forces, it is unlikely that our Afghan allies took the effort to destroy all sensitive material. Thus, the Taliban likely captured many computers and now have access to databases that the US and its coalition kept in Afghanistan. This captured data, both electronic and hard copy, includes details of military, diplomatic, and intelligence activities, not only in Afghanistan but across the entire region.
This will make interesting reading when the Taliban publishes them, as they certainly will. Some items will merely be embarrassing, such as the many complaints about corrupt Afghan government officials. This will resemble the WikiLeaks publication of documents stolen by then-Private Manning, where the gossip about world leaders was tantalizing but ultimately of little significance. More serious will be publication of the names of Afghan and US intelligence officials and details about ongoing operations, because these will damage US security and may be fatal for the Afghans. The precedent here is the 1979 Iranian revolution, which painstakingly reconstructed shredded US Embassy documents and published sensitive and sometimes embarrassing details about US intelligence operations.