Haha...you think Russia is gonna let China install a puppet in NK? You do know that Russia fought wars to block the Chinese from getting direct access to the Sea of Japan and the Sea of Okhotsk right? Take a look at The North Korean border. You see how Russia surrounds East China and NK blocks China from those seas? If you didn't know, now you do.

Also you think the nationalists of South Korea will let any part of Korea go to the Chinese? The Koreans still want the large chunk of Manchuria back that was given to the Chinese after the Japanese ceded that part of land in a treaty. Just a side note...the UN declared that treaty null and void and will probably give that land back to a unified Korea if there was to be a problem with China and the U.S.

Also, you make it seem like South Korea isn't prepared to rebuild NK. You make it seem like all doom and gloom when it is quite the opposite. They've been saving up a huge fund for such an event. Now that South Korea has caught up with the world in terms of technology (also a leader in many ways), what makes you think companies like Hyundai and Samsung won't take advantage of such a huge surplus of natural materials and rare mineral deposits of NK (some of the greatest amounts in the world).

I think a unified Korea (with parts of Manchuria restored) would be a great thing. Why fear it? We need the balance of power to change in Asia and I trust the South Koreans way more than the Chinese as do the US.