Until we leave, there will be a slow but steady stream of dead and maimed American troops coming home in coffins and on medevac flights.  Whenever we do finally leave, the country will collapse into chaos, whether we do it next week or twenty years from now.  Just a question of how many dead and crippled young men and women, as well as billions of dollars of tax payer money, we want to throw away before we finally admit we may may be able to kill bad guys (plus women, children, etc) but we can't build a functional state there, and once we shifted our intent from A to B we had already lost the war in Afghanistan.