A conventional war with the DPRK would not last very long. At best, they operate equipment whose hayday was in the 1960's. There is, however, a LOT of it. If they could achieve strategic surprise and successfully deploy their large 'special forces' units, they could make a mess of things for a day or two.
But they have nothing that could even come close to matching what happens to them when SK, Japanese and US airpower gets involved.
The 'war' part of a conflict with the DPRK is the 'easy' part to deal with. How Russia and China react is a complicating factor... Add to that the massive humanitarian crisis that happens after the DPRK's government is gone. THAT would be the expensive and complicated part.
All IMHO, of course.
"Unlike most of you, I am not a nut."
- Homer Simpson
"If the enemy opens the door, you must race in."
- Sun Tzu - Art of War