I think that the real issue w/NK has nothing to do with needs (it doesn't even really risk being invaded over going nuclear as events have shown) and everything to do with wants (missle tech sales, foreign aid extortion, etc..). Whether, as you say, NK doesn't want to rely on the PRC or not is irrelevant b/c that's likely a key reason no one's going to invade them. China tolerates NK behavior b/c it keeps the region and the US slightly off-balance. I don't believe they're truly that worried about a mass exodus from NK flooding across the border (what? China can just shoot them like it does its own citizens
) or any of the other "joys of having a dirt poor neighbor". As to your point about the ROC vs NK, I'd say that's the irony. The ROC, with a better claim to worry about invasion, can't have them precisely b/c the PRC would likely see that as grounds for an actual attack. Meanwhile, NK arms up while the rest of the world watches and effectively does nothing.