More like South Korea shifts more towards China. Japan would likely do the same; they have no more love for the North than South Korea has. If either country concludes that they can't depend on the U.S. to be there in the event of North Korean aggression then they will have no other choice.
I always suspect the end-game is that China goes to South Korea and says, “We’ll take care of the North Korea problem for you.” The US gets kicked out, and the united Korea is firmly in China’s orbit.