I don't see how leaving without decapitating the regime would get us anywhere near our objective, which is solely to keep our country safe from future attacks. What would it do to prevent another Arab warrior to set up a kamikaze camp somewhere else?
I agree that the imperialist course is replete with perils that you outline. The right imperialist course is one among many wrong imperialist courses. The right course means establishing either an occupation regime or a puppet government that sees as its central function enforcement of basic rights: right to life and property, -- the same rights that the terrorists violate. It should be supportive of indigenous culture and religion, or religion-blind. I believe that we have resources to accomplish that, provided that the silly government programs that waste our money today domestically, are deep-sixed.
I think that it would behoove us to simply decapitate and wait. If a movement emerges that we could support, then do so. If not, let it stew until the Afgani people do something about it. Decapitate again as necessary. To impose order merely sets us up for an endless morass and bogs down our strained resources. We are doing it in Bosnia. Haiti was a real winner. Try doing the same thing in Pakistan for example, or Myanmar, Zambia, Angola, Iraq, Iran... Our national government simply does not possess the power to do what you suggest and still meet its primary commitment of national defense. It does however have the power to assist an indigenous movement. That is why Osama Bin Laden's murder of Shah Massoud was so significant. I don't doubt that he had help on that one and we had better work on investigating that carefully. Any guesses?
So, IMHO, we must rely upon the Afgani people to find that leader. Not to do so is in my judgement immoral and therefore likely to backfire.