Perhaps then, the question is how much of the responsibility lies with the South after such a thing occurs. Would SK simply annex NK or would something like a joint/international humanitarian effort to help NK survive and may be start its own government be better?

Honestly, I don't have any right to say one way or the other is right because I'm not even Korean, I just think that we in the west need to stop taking as a hypothesis that if NK collapses that it is SK's responsibility. I think it is up to the South Koreans to decide whether they want that, and not us [1].

[1] And yes, that's what this article is about, the government is preparing for this contingency, but as we in the west know, our government doesn't always do what we want.

Not just the South, but China too. North Korean refugees are already a concern for China.[1] If the economy or the government collapses in North Korea, it's not hard to imagine chaos spilling over in to both countries.

[1] http://blogs.piie.com/nk/?p=13422

I wouldn't think that "order" is what they'd like to maintain. But rather, keep the humanitarian crisis just past it's border from resulting in millions dying.

The economy of the north already collapsed in the 1990s, with on the order of 500,000 people dying from famine. But this did not break the regime.