Even when they can hit everywhere on this planet, their limited budget and production capability will not allow them to produce more than a few of these missiles as well as the payload. There is not much of a concern. It is not like the Fat Kim Dynasty is actively seeking suicide. They just want to be left alone while ruling over their people like Kings... wait, they are kings. On the top of the unrealistic goal of absorbing South Korea. If anything, it will be the South absorbing the North when North collapses on its own.
I have the same assessment of the situation in North Korea which would no doubt face am implosion in future instead of an explosion. I bet that the North will end up convulsing along the faultlines of deep internal rifts amongst the ruling classes as they compete for hegemony and attempt to find a common grounding in this tightly controlled place. A grave pointer to serious pointer is the removal of Kim's uncle, a high ranking bureaucrat from a public gathering and subsequent execution