The buildings can be rebuilt. Hopefully, the people will be safe in the bomb shelters.
As for the North Korean artillery, I would think that few cannons will get off more than 5 rounds due to counter-battery fire. It is relatively easy for a modern army to identify the position of the cannon from the trajectory of the round. The question is how fast is the response time. With drones in the sky, response could be very fast. But, even with conventional artillery, response would quickly suppress if not destroy the enemy’s artillery.
Attacking South Korea’s civilian population would probably make all-out war inevitable, and North Korea would certainly be crippled if not outright conquered by South Korea in an all-out war.
The north’s military is equipped with a mix of late 1950s / 1960s weapon systems. We’re talking T-62 and T-54 tanks, and MiG 21 fighters. In contrast, the South Korean weapon systems are modern. Their K1 tank is a somewhat down-sized knock-off of our M-1. With regard to air assets, they not only have a qualitative advantage, they also have considerably more. The prospect would be of qualitatively superior ground forces operating with air superiority.
The first echelon of the North Korean army - about a million strong - is dug in just north of the DMZ. They would be hard to displace. But, any attempt on their part to maneuver would be fatal. They could be by-passed and the loyalty of the starving masses in the area to the north could be tested.
The masses have been heavily indoctrinated from birth, and are supposedly organized into a reserve force of 7 million. But, the regime cannot be confident of the choice they would make if they were given a choice.
The real fear of the U.S. is that South Korea, which is entirely capable of defending itself, makes a decision that we wouldn’t want them to make. Hence, the President, in saying that we will defend South Korea, was really saying he doesn’t want South Korea to defend itself.
With regard to China,.South Korea is China’s #1 trading partner. China has a lot more to gain, economically, from a reunified Korea; then a whack North Korea offers. As China emerges as an economic powerhouse, with extensive global trade and investments, its interests in peace and stability in the world increase; and, its need for rogue client states diminishes. North Korea cannot be confident that China will support it.
Whatever you said about need for rogue states would be true for a representative democracy, but not for the PRC. North Korea, Pakistan and Iran have kept potential Chinese rivals bleeding for decades and will continue to do so. The last thing China wants is for them to be taken out of the scene. ‘Peace and Stability’ are relative terms. If stability means a weakened India or Japan, that is why China continues to support Pakistan and North Korea.
You are right-China doesn’t want to destroy trade with South Korea. Which is why the North fires off a few rounds and then steps back. Do you seriously think anyone-including the US, China and South Korea want reunification?? Even a completely peaceful reunification will hit the South Korean economy hard given North Korea’s current shape. Would any sane country want to add 23+ million dirt poor people to their population. So who will foot the bill??? Reunification in the current term is a fantasy.
About the military factor. Again as you pointed out, North Korea’s conventional forces are obsolete. The only problem is that they know it better than anyone else. If they tried to invest in rearming themselves conventional, they would have spent themselves into oblivion. Which is why they have invested in asymmetric capabilites. Artillery, heavy anti-aircraft capability, special forces (the world’s largest number), cyber warfare, NBC weapons. So again, do you think the South Koreans would want to risk even a limited war which could potentially undermine years of economic development. As I’ve said before, the only way South Korea can come out with relatively little damage is if the US nukes North Korea, which probably wont happen. Or if there is a coup in Pyongyang.