"I recently conducted a quantitative assessment of the economic impacts of unification on North and South Korea under several hypothetical scenarios, assuming North Korea’s sudden collapse. As it turns out, a peacefully managed unification process, characterized by comprehensive economic reform and opening-up, could enable North Korea to achieve sustained double-digit GDP growth, despite a sharp slowdown immediately following the collapse...
As for South Korea, with sufficient preparation, effective policies, and more financial resources, it can manage a peaceful reunification and mitigate the adverse effects of the shock."
http://economia.icaew.com/en/opinion/august-2017/planning-for-korean-reunification
The regime has been propped up for decades by China and Russia. What do they want more; a criminal dictator with Nukes on their border who can be a thorn in our side(increasingly theirs as well, A withdrawal of US troops from the Korean Peninsula?
I think that if the US and SK put that(A US withdrawal following Korean reunification) on the table as an option at any future date then China and Russia would be much more willing to put more pressure on Kim's nuclear program and much less concerned about the potential collapse of the regime. Their worst case scenario is a unified Korea that extends US strategic superiority. We can not only remove that fear but offer them a little more breathing room in that eventuality.
We don't need to plan for how to make the regime collapse but if we can come to a clear and aceptable understanding with China and Russia about what we will do if it were to happen we will likely open up more options.
With Kim's patrons on the security Council becoming increasingly less interested in supporting him Kim's desire for self preservation may make him change course.
Kim does not need a nuke for the sake of a deterrent. As has been pointed out time and again his conventional arsenal and standing army is more than enough deterrent. His Nukes are for the purpose of having an offensive posture. Their purpose is to threaten his neighbors and the US in order to get what he wants. That's a dangerous posture that will only escalate. We can't invite him to the big boy table simply because he is agressive and dangerous.