The survivors simply live on, but now in abject poverty.
Afghanistan has been through this recently ~ the Soviets came in and crushed the country. Then they left ~ the Afghans thrashed about killing yet more millions and then AlQaida came in.
Osama Bin Laden took Afghanistan into very dangerous waters ~ so we crushed them again.
It's time to put a stop to this cycle.
New leadership usually rises from within, not without. (OBL in Afghanistan was an anomoly).
Nation-building worked in Japan and Germany after WW2 because they were civilized, technologically sophisticated, first-world nations whose tribal feuds were long over. It should've been obvious that it cannot work in an environment where Islam thrives, but folks are beginning to catch on.
Islamics comprehend only strength, and view our attempts at "winning hearts and minds" as weakness. Sensing weakness, they're less likely to go along with the master plan out of a lack of respect. So all we can really do is keep destroying threatening regimes (without policing them for years after the fact) until they comprehend the situation -- join the civilized world or die.