The problem with this is that N-Korea doesn't just have Kim Jong Il.
Actually, Kim Jong Il is the only thing standing between the world and N-Korea's military hard liners. This latest nuke test is to placate his own national military as much as it is to play nuclear brinkmanship on an international stage.
Kim wants to move his son into a position to follow him once he dies. He also wants to stay in power. To do this, he needs the military to back him. The military is hardcore. Thus, he gives the generals a bomb to toy around with.
Kim actually is the one certainty the world has in dealing with N-Korea. By now we know this guy, we can manage this whole mess with him in place (not solve it, but at least manage it). With Kim gone... who becomes the new leader? Some random admiral intent on chemically bombing Seoul and Tokyo?
Certainty is a great good in international politics, since uncertainty brings volatility and conflict.