They will still be there, helping and assisting, but the Afghans have to do more dying then the Americans. In 2013 you might still hear of kidnapped American aid workers, held hostage or killed on videos. But American troops pulling out is a start to letting Afghanistan have more autonomy in its internal affairs. I think that since America left Afghanistan alone after the Soviet invasion failed, Afghanistan floundered, and lashed out at its former backer. Now America has tried to fix Afghanistan's floundering by force, they can do not much else forcefully but let the seeds they sewed grow; However Afghanistan isn't going to be a quagmire of American foreign policy like it was to the Soviets, who cut and run from their invasion.
America will clean up the best it can cause it saw what happened to the weapons that the USSR left behind, they became the weapons that the Taliban
was using against the Americans. America will pull out its troops and leave advisors to clear up any expended but unexploded munitions, make sure the
Afghanistan forces can fight for themselves.
It doesn't want to withdraw in a hurry because when the USSR withdrew in a hurry it left behind loads of equipment that bit America in the butt,
since it fell into the wrong hands. America withdraws, shoves weapons into what it believes will be the right hands.
Time will tell.