There are other ethnic groups over there, too, Tajiks, Uzbeks, lots of other non-Pushtuns, it is possible that those groups will be willing allies, and likely that they will get support from their ethnic homelands.
Afghanistan is not a homogeneous place, there is a sizable Iranian/Persian minority there, and they had deep ties with the Northern Alliance.
They also have a much better motivation to fight and win on account of Afghanistan being able to choke off a strategically important portion of their...
So, apparently in 1998, due to a host of incidents and disputes, Afghanistan almost got invaded by Iran, with the Iranians massing over a quarter million troops on the border.
What would have happened if Iran had invaded?