Kim Jong-un has been so cocky and confident(at least in public) that he will definitely push the envelope. From his point of view, he is so close to the ultimate prize, maybe less than a year away. I don't think he will slow down if U.S. and China go about their way as they do now: passing bucks, blaming each other, with no real action from either side.
You are right that there might be accidents either at their nuclear bomb site or perhaps at sites for production of chemical WMD. However, the effect of these are probably limited in scale. An accident at a production facility for biological weapons, as well as a pandemic flu or similar might have bigger impact due to the bad health ad food situation in NK.