all done...
If they detonate it in South Korean waters, it's all over for the north. Nuking an American ally means that the USA WILL end the regime, nothing else can be contemplated by Washington.
And decision makers that are captured will never again be free--if they survive. And--the consequences for other rogue nuclear wannabe states will be severe. I don't think that there will be any remaining tolerance for nuclear programs in states seen as likely to use them--one did, so that djinn is out of the bottle...