Those were the two reasons we invaded Afghanistan -- to defeat AQ and kill/capture OBL. Had we caught OBL at Tora Bora in 2001, then declaring victory and leavingin 2002 might have been our best option. But that didn't happen, and the worst possible result for us would have been to "declare victory" in 2002 -- as this author claims we should have done - only to have OBL pop up out of some hole and start thumbing his nose at us all over again.
Couldn't leave until we got OBL. That happened in 2010, so if you're looking for a time to withdraw, it would have been then.