I think the strategic rational for unification completely swapped about 20 years ago. Up until the early 2000s it was likely in South Korea's, and the US's, interest to find a way to topple NK and unify the peninsula. The two populations had blood ties and common culture. Technologically the gap was growing but still reasonable. It would have been close to an east/west Germany type of situation where unification took effort but ultimately was clearly beneficial. China (and Russia) would have been losers in that unification would have brought a western friendly government even closer to their border. Additionally, NK still had a chance of re-energizing and becoming a real threat to SK.
Now however NK is in such bad shape that unification would be traumatic. South Korea would take on a problem of epic proportions, caring for and bringing a population of that size back into the broader world would be exceptionally costly and definitely not guaranteed to end well, possibly destabilizing SK in the process. Their cultures have grown apart making it hard for them to understand each other. The blood ties are not really there anymore. China and Russia would likely be the winners in that everyone sees NK as crazy and anyone helping them is hurting the world so they could get rid of that baggage. China especially would gain by having rail access to massive shipping assets to deliver goods even cheaper to the world. Finally, the US would loose a major rationale for stationing forces that close to China. They could, rightfully, say that NK isn't a threat and the massive US assets in South Korea and Japan should be drawn down.
Sadly we know from events in Ukraine that NK artillery works and that they have plenty of it. Yes, it's poor quality, but far from harmless.
Also to be clear: artillery is not exactly rocket science. They idea that NK doesn't have huge stockpiles is ludicrous.
But even so, if there was a serious threat of war, which is unlikely because China would stop North Korea, the US would place assets in the region and as we got close to a confrontation the US and South Korea (and as things are looking, probably Japan) would begin an aerial and missile bombardment to destroy in place North Korean offensive capabilities. Some would get through of course, perhaps thousands or tens of thousands of South Korean casualties, but in the context of a conventional war North Korea's capabilities would be quickly overwhelmed, at least in my opinion.
But honestly, the current status quo works pretty well for everyone except the people of North Korea, but there's not much we can do. It's a tragedy and the blame for that falls squarely on the Soviet Union and Chinese Communist Party.