In terms of weapons design, it could go either way and both sides have persuasive arguments. From a standpoint of policy, that’s not good news for the North Koreans. A fizzle diminishes the deterrence factor of a nuclear weapon — especially since both Japan and South Korea will almost certainly be able to possess working nuclear weapons (probably with large MADE IN THE USA stamps on them) in short order if so desired. Given that the DPRK can’t get it up (its missiles at least) and can’t prove they have a working nuke, beyond the initial shock of a DPRK nuclear test, there’s not much else.
All in all, this was probably a major strategic mistake for the Kim Jung Il regime. They’ve been pulling the tail of the Chinese dragon for a long time now, and if the Chinese start saying that enough is enough, it’s quite possible that the Chinese will start really playing hardball — as in having PLA agents start assassinating leaders and disrupting the regime. Quite frankly, that’s not at all a bad thing for the rest of the world. In fact, that’s probably one of the few truly effective things that can be done about the situation.
This does reflect badly on American policy, however. President Bush had been talking a tough line about not letting North Korea get nuclear technology. Granted, there’s not much we could do other than risk a major destabilizing war that would leave South Korea a smoldering ruin and risk major attacks on Japan as well. However, there can be no doubts that the Iranians are looking at our reaction with great interest and it is perfectly fair to ask whether we’re really serious about counterproliferation. As they say, talk is cheap, and if we’re not willing to take real action to prevent the spread of deadly weapons to rogue regimes, then we’ll have to live with the consequences.