IMO, there's no other way for it to end.
Without strong American leadership, there is no other way for it to end, but think of what that means. If Afghanistan falls to the insurgents, it will be used as a base to wrest control of the tribal lands in Pakistan from the Pakistani government, and those lands will be used as a base of operations to try to gain control of the Pakistani government and its nuclear arsenal, putting hundreds of millions of people's lives in Pakistan and India at risk.
These people are suicide bombers who crave and glorify martyrdom and who seem to have no concern about the innocent lives they destroy as they pursue this goal. If they did gain control of Pakistan would they be deterred from a first launch by the certain devastation that would come with an Indian retaliation? These people are suicide bombers.
And what of US security? Would nuclear devices make their way from a radical Pakistani government into the hands of terrorists who are set on attacking the US or our allies? What if those planes had carried nuclear devices on Sept. 11: we would not have just lost the World Trade Center and part of the Pentagon, we would have lost New York City and Washington D.C. Would a radical Pakistani government be deterred from abetting such an attack on the US out of fear of our retaliation? They're suicide bombers.
Responsible nations, like responsible people, sometimes have to do things they really don't want to do because they understand that their long term prospects are greatly improved if they do these things. There are no unsolvable problems in Afghanistan, only complications that increase the cost and may lengthen the duration of the mission, which is to help establish a stable democracy that will not allow international insurgencies such as, but not limited to, al Qaeda to establish bases of operations from which to attack the US or its allies or Afghanistan's other neighbors. Nearly everyone is the world would be better off if this mission is successful, and there is no reason to think it can't be successful in time if the US shows the kind of strong leadership and commitment to the mission that will give the various factions in Afghanistan confidence that we will not abandon them to the insurgents or to a corrupt, despotic government.