The resulting confusion in the hierarchy would be interesting, to say the least. Kim Han-sol, Kim Jong-chul, Ri Yong-ho, Kim Ju-ae loyalists, and Choe Ryong-hae would presumably all compete for power. I think whoever Kim Sul-song sides with of the Kims would dominate in a short struggle for leadership.
There's always the possibility Sul-song herself takes over, at least maybe claiming to be a regent for Ju-ae, but I'm not sure how the populace and military would react to a female leader. Han-sol would gain the backing of South Korea, and possibly even China. If the Chinese allies in the government and military and the Chinese ambassador made it clear that they preferred Han-sol, it would be interesting to see what the remaining North Korean leaders would do.