As an ex-military member, a large (nuclear based) EMP pulse would cause significant damage to our power grid and nonmilitary graded equipment, but is recoverable and would not take that long to recover key components (6 months). Doomsayers aside. NPK has no followup strike capability.
Fortunately, the NPK doesn't have that level of nuke capability. They have only demonstrated a low yield nuke. Additionally they have not demonstrated they have the miniaturization capability necessary to launch a ICBM based nuke.
If they managed to do this and actually followed through, our response would be overwhelming. North Korea would cease to exist. The current regime would be destroyed and they know it. They exist to preserve their regime. The leadership is not ideologues, they are parasites on the Korean people and the world.
Kim and his generals are not suicidal....They want something, more free food aid etc.
What would the country look like after 6m it takes to recover key components of the grid?
Do you have clean water and food set aside for the engineers that would be responsible for building that stuff out?
It was dicey after 6w in rural MS without power. Imagine a big city.