Some sort of "soft" landing, e.g. Kim's death from health-related causes (Ahem!) and a less oppressive government by the military would probably be the best solution. I don't think anyone wants a violent revolution in North Korea; especially the Chinese.
Soft-landing is what everybody wants, but Kim Jong-il does his best to cut off any avenue to lead to soft-landing. The situation conducive to soft-landing is also a dangerous setting for Kim's regime, because it means that alternative to Kim's regime is available and ready.
That is why the change could come with little warning. It may not be a violent revolution, but it would at least entail short period of intense uncertainty and high anxiety.