massive retaliation literally destroying their country
I assume you don't actually know where NK is. Look on a map. Bejing is less than 500miles away. NK shares a border with China. Japan is very close, too. There is no possibility that China would allow the USA to nuke one of its neighbours - not with the possibility of fallout spreading across the region.
Luckily, your fears are completely unfounded. NK doesn't give a flying *** about the USA. It is more concerned with South Korea and if it was to use a nuke, they already have a target painted large as Seoul is only 30 miles from the NK border - easily reachable by truck in less than an hour. That is their hostage, should anyone attack them. What is far more likely is that they are developing the technology to sell. The launches are just advertising for their capabilities and the people you should be worried about are the ones who hate you and have lots of money. Sadly, that list is quite long: just look at all the countries you've bombed back to the stone age in the past few decades.