But you're not counting the "Chinese volunteers" who completely turned around the result of the initial war. After they withdrew, it's very questionable the North could have fought some more.
> it's very questionable the North could have fought some more
China didn't enter the war "just because" - the main reason was the US encroachment on the Chinese border. By comparison, it would be as-if China was warring in Mexico, and the US decided to ensure China didn't continue marching northwards.
Both China and the US more-or-less stood-down together, which left both North and South Korea in a tough spot - fighting could absolutely continue, however it would have been more of a drag on both nations without their "big brother" support.
So, the ceasefire wasn't because one side of the other couldn't continue the fight - it was because both sides _could_ continue the fight, but both recognized it would be devastating for everyone.
If we fast forward to today, it's unquestionable both sides (with or without foreign support) could continue to wage war on the other.
Well, it's demonstrably not "unquestionable", since I question every paragraph you've written above after the first.
And most especially the last, for the North can't even feed its own army, and one of the many things standing in the way of reunification is the major difference in intelligence, height, and so on of the respective populations, the North being stunted from malnutrition.
The South's hand has been stayed because they've not been willing to take the costs, especially to Seoul, infamously within heavy artillery range of the North, and of course our moderating influence. And now, of course, we've let the North get nukes....
However, one should note that they're part of a worldwide network of nations trying to achieve nuclear status sub rosa, they're definitely not doing it all by themselves. And of course their nomenklatura that's executing this nuclear program is by definition not starving. But the bulk of the nation is, and rather uniquely, that includes the army, and that has decisive implications on their ability to wage a general war against the South.
I'm a bit skeptical. North Korea is a highly militarized state and highly dependent on military control. Surely if the military itself is starving we'd see much greater instability than we actually do.
The most important reason the North can't reasonably go to war with the South is that the South obviously enjoys US support and nobody would support the North in such an invasion.
I don't know how the DPRK does it (it's notoriously opaque), but it would be astounding if they didn't follow the 20th Century Communist model of having political types police the military. As for the Korean People's Army, a few minutes with Wikipedia turned up this acknowledgement of direct political control (https://en.wikipedia.org/wiki/Korean_People%27s_Army#Commiss...):
The primary path for command and control of the KPA extends through the State Affairs Commission which was led by its chairman Kim Jong-il until 2011, to the Ministry of People's Armed Forces and its General Staff Department. From there on, command and control flows to the various bureaus and operational units. A secondary path, to ensure political control of the military establishment, extends through the Workers' Party of Korea's Central Military Commission of the Workers' Party of Korea.
Now, this control is not tight like the infamous USSR Red army political commissars (https://en.wikipedia.org/wiki/Political_commissar#Red_Army), as can be discerned by how nowadays army units out in the field on non-military duty are known to act like bandits. Including capturing and eating small farm animals before they have to return to their barracks.
So, yes, a degree of skepticism is warranted, but there are too many reports of this sort of thing to dismiss it. The Soviets certainly squared this circle, albeit without the spur of pervasive malnutrition ... which, come to think of it, can put a damper on mutinies and the like, if you barely have enough energy to survive.
The Soviet approach to civilians, making them spend lots of time gathering the necessities of life, is another way of suppressing dissent. The PRC was more direct, get on the wrong side of your block or village political committee and you'd no longer get your ration coupons and would starve to death. My PRC roommates in the very late '80s reported this was the biggest effect of Deng Xiaoping's opening of the food system, changing your fate to having to pay more for a lot of your food.
