OTOH, a Taliban reconquest is unacceptable too. I think the best option is to wait out the Karzai government, keeping it alive and in power in the major Afghani cities at the lowest cost in blood and treasure, until a competent government is in place. Kind of like the Soviet strategy in Afghanistan - hardly the greatest selling point, but as Matt Yglesias points out, we've got advantages that the Soviets didn't.
While I don't usually have a high opinion of Joe Biden, he had a great point that we're focusing on the wrong country by putting 95% of our money into Afghanistan relative to Pakistan. If minimizing our effort in Afghanistan could redirect some of it to Pakistan, all the better.
The long-term solution for Pakistan, as far as I can tell, is development (same answer I had before). Not a quick solution, but maybe Pakistani society will look at how India is doing so much better than they are, and get inspired/threatened enough to make a change.