Reading the tea leaves from North Korea is something akin to trying to accurately divine the future from the entrails of a frog. In short, it's a mess.
We know so little about Kim's successor, his third son Kim Jong Eun, that there isn't much intelligent speculation about how he would rule.
Then again, what we do know is pretty scary. Wall Street Journal:
The portrait of Kim Jong Eun that emerges in his U.S. profile is that of a young man who, despite years of education in the West, is steeped in his father's cult of personality and may be even more mercurial and merciless, officials said.
A senior U.S. official said intelligence analysts believe, for instance, that Kim Jung Eun "tortured small animals" when he was a youth. "He has a violent streak and that's worrisome," a senior U.S. official said, summing up the U.S. assessments.
U.S. spy agencies and diplomats routinely prepare classified assessments of foreign leaders to guide U.S. decision making.
Constructing a complete assessment of Kim Jong Eun has been a particularly difficult undertaking because he has spent most of his life in North Korea's insular culture.
Allahpundit at Hot Air refers to the transition as "From Tiberius to Caligula." That, along with the very real possibility that Kim Jong Eun is not in charge and the country is being run by the military makes things a little dicey for South Korea in the near term. However, it is not likely that the North Koreans will attack a country that is keeping their people from starving to death. More likely, we will hear a lot of bombast and empty threats as the succession process works itself out.