The best client state is the one with shared morality, not from being a financial burden, no matter how feasible it may be. Contrary to popular belief, the worst kind of dependencies are only two: food and energy. Defense dependency is a far third. That is why the US built Japan's and South Korea's economies to the point where there came a diminishing dependency on outsiders. Today, contrary to the delusions of the Chinese members here with their incessant 'thermonuclear' masturbation, either South Korea and Japan can give the PLA a run for its money. All three: US, Japan, and South Korea, have a shared morality. Give enough time, the relationship ceases to be that of sponsor and client but allies and even friends. No matter what the Chinese members here may say about Japan and South Korea, both of them are closer to the US in terms of being allies, or even friends, than China can say for North Korea.
So even if North Korea can somehow survive our lifetime, which I doubt given what I saw when The Berlin Wall came down from only a few years earlier when I toured it, the China-NKR relationship will never evolve beyond sponsor and client. The Chinese government will always view NKR as a geopolitical burden, not an ally, and one that sucks at the Chinese teat while giving micrometers next to nothing in return.
Congrats on your naivete.