The only way the civilized world is going to limit the cost of dealing with the ultimate war with N. Korea is to prepare S. Korea, with the help other friendly countries, to do a massive surgical strike to take out the entire N. Korean military and its facilities and have S. Korea able and supplied and armed with its own people who can move in to supplie staples and organization to the society.
I am not convinced the military which is ultimately in control of everything, will ever give up its power, no matter what the "Glorius Leader" says or does, as he can be replaced.
You let the cancer grow or you cut it out and deal with the consequences. Of course this could never happen within the next 4 years because of leaders in power now who have no vision other than their own personal power.
We certainly have battle plans ready that would allow us to militarily unify Korea under the south. There would be nothing "surgical" about it, though. North Korea has massive numbers of troops, rockets, artillery, etc., and South Korea's capital is only 35 miles from the border, within range of the larger NK guns. Here's a map of what could happen. Seoul would be a pawn in the battle, and it would destabilize the entire area for some time.
I think the fundamental question here is whether this is a show of strength being done because North Korea wants to talk but has nothing else to negotiate with. If so, perhaps you meet them, acknowledge their big scary threats, trade around for some perks (maybe make Kim Jong Il the equivalent of the British Royal family in the new Korea, with a figurehead role), and unify them peacefully with everyone coming out ahead. On the other hand, maybe they want to remain independent and hold a nuclear threat over the United States' head... in which case better to strike sooner, before they have the capability. I don't have any of that information, so I'm not going to second-guess the decisions.