North Korea is in a tough state. Their people are starving, their healthcare is trash. A huge population of their people are blind.
Also, Russia is backing U.N. sanctions on North Korea.
It's hard to say, at this state North Korea seems to be dangerous. I'd rather see North Korea successfully establish a working system beneficial to it's people rather than staying in their state of war mongering and starvation. They have a lot to come back from.
It is well accepted by the respectable international community that it is only a matter of time before North Korea falls from political instability. It is already showing signs of it with Kim Jong-un executing this uncle, the second most powerful man in the DPRK. His uncle was also the man China, their only significant supporter, liked to talk to diplomatically. China (or anybody for that matter) does not like to talk to Kim Jong-un because he is too unpredictable and lacks certainty when it comes to relations.
By "near future" I mean probably a couple decades or so, but it is inevitable. North Korea lacks almost every vital resource including raw manufacturing materials, food, energy, money, and so on. They get the majority of those resources from China who wants to see them continue on for as long as possible but even they see the DPRK as an international nuisance. Unfortunately, China likes them because they're strategically convenient because they serve as a "buffer zone" between their border at the Yalu River and the American allies, the ROK and Japan, to the east. China also doesn't want to have to deal with the likely millions of North Korean refugees that would flood over their border from a violent political collapse of the DPRK.
It is obvious to see that the DPRK is not a lasting country due to apparent instability, a society not well designed for the long-run, and their sheer isolation that is causing them to drastically lag behind the world around them. Their society is incredibly behind that of other nations in development in both technology and society. The UN lists North Korea as a developing country under the standard that they have "large-scale breakdown of rule of law or non-development-oriented dictatorship" and they are a "failed state".
There is no way that they could dominate another country militarily, including South Korea. Economically, they would not be able to afford it. With their military idling as they are the DPRK still spends an estimated 20% of their GDP on their defense budget! In comparison, the United States, having the largest defense budget while actively fighting a global war on terror, spends about 4.5% of our GDP on our military. If North Korea wanted to wage a an all-out war they would have to raise their budget significantly forcing catastrophic budget cuts elsewhere that would quite possibly lead to their national collapse. North Korea can, right now, barely afford to feed their military much less afford an invasion campaign.
Also, the international community, especially the UN Security Council (perhaps excluding China) overwhelmingly support the ROK. The United States has about 28,000 troops deployed in the ROK as well as military installations. There are also UN forces in South Korea as well.
Ultimately, there is virtually nothing realistically going for the DPRK lasting into the distant future or being successful in any of their radical goals.
The likelihood of this happening is unlikely as you got some guy named Kim Jong who is going to rule North Korea straight up until he goes down which is not so distant but eventually in the faraway future when he discovers the Fountain of Youth and Immortality, which is also unlikely is when they will fall to down deep pits of Hell; but still, they will remain how they should be able to be remaining up here in now.
The fact that the DPRK has remained unwavering in the face of international intimidation just shows that the DPRK is a country that will remain for centuries. I'd say that in the near future it will absorb the South and unify the two Koreas finally. The US and its allies will try to collapse them but they will fail.