Afghanistan will be fine. There is a prison break and the Taliban took a few villages, oh no, the same has happened every year. Kaplan is just alarmist. The truth is Afghanistan will never be perfect, it has never been perfect, there will always be rebels there. Thing have gotten progressively better in Afghanistan since 2001. The entire coalition strategy there is one of inches. They slowly consolidate an area, and then move on to another. No big amazing victories for the newspapers, but real honest to god progress on the ground. The North and West of the country are relatively calm, all the problems are on the Pakistani border.
Of course the troops there could use a lot more men and resources, and that would help them accomplish their job a lot better and a lot sooner. But with what they have now they will succeed. The end result may not be a perfectly stable country (think more like Colombia with FARC), and it may take another ten years, but in the end Afghanistan will be weak state. Not a failed state, but a weak state that works. In the case of Afghanistan a weak state may be a job well done.