Is North Korea's Leader losing it?

[Seamus Fermanagh]

...

Are the countries named as part of the UNC all technically still at war with North Korea, and would they be obliged they reaffirm their commitment in that capacity to the coalition in the event of renewed hostilities?

Arguable. The NK has publicly declared itself not bound by the agreement on several occasions. Moreover, the USA broke the agreement back in the late 1950s by introducing new weapons systems. So, while the UNC members might be morally obligated, at least the way I interpret things, there is more than enough legalistic grounds to tell the USA and SK that they are on their own.

[Montmorency]

This is the last opportunity to prevent them becoming dangerous to everyone not bordering it.

Exactly. Another (rough) way to present the logic up until now:

Spoiler Alert, click show to read: 

Arguable. The NK has publicly declared itself not bound by the agreement on several occasions. Moreover, the USA broke the agreement back in the late 1950s by introducing new weapons systems. So, while the UNC members might be morally obligated, at least the way I interpret things, there is more than enough legalistic grounds to tell the USA and SK that they are on their own.

Here's some comments from an old article on Canada's potential role:

1. Canada has no real combat element in Korea and Japan (as of 2010), being represented in the relevant offices by a handful of COs and their staff.
2. The legacy UN mission will probably not be given formal permission to do this or that, with Chinese and Russian intransigence on the SC to be expected.
3.

"I have a hunch that the UN role, whatever its formalities are now through the military commission and other things, are likely to be superseded almost immediately by a coalition of the willing that would be led by the United States and South Korea."

4.

Federal officials say there have been no "asks" to Canada for military support in the region.

On the other hand, with challenges having grown on all ends over the past decade a desperate United States could come down to entreating or demanding various allies for boots on the ground.

On the historical end, this essay points out that UN resolutions up to the war were intending to create a "Unified Command" designating the United States as executive agent, but the US did not like the appearance of acting unilaterally and so it began to be designated a "United Nations Command" as a sort of camouflage. This is despite the UN violating its own charter at least twice. First in accepting that there would be no UN political oversight of a mission under the ostensible auspices of the body. Second in that Harry Truman acted unconstitutionally by committing troops to the conflict in terms of a "police action" before getting Congressional approval, and UN members participating in UN military actions are required by the UN charter to act in accordance with their individual "constitutional processes".

[HopAlongBunny]

Further to "China moving into the spaces vacated by the U.S."
Besides the Pacific Rim, look to the U.N.. Trump's isolationist rhetoric and withdrawl from international engagement has opened up space for China.
Brave New World with China in the lead? Not yet, but if China is willing to pick up the slack, I don't see much opposition from the U.N. membership:

http://foreignpolicy.com/2017/10/06/...fill-the-void/

[Seamus Fermanagh]

No opposition is likely I agree. I suspect the bulk of the world leadership would prefer a second "Great Power" and would much prefer China to Russia in that role.