If South Korea goes over to China for $4 billion dollars, that itself is significant.
Do you for one second believe that South Korea would willingly go over to China?
Before that ever happened, they would probably enter into a mutual assistance treaty with Japan and possibly with Taiwan, Indonesia, or even Australia and/or New Zealand, forming a new and meaningful “SEATO” organization.
If South Korea goes over to China because they feel that they can't count on the U.S. then that's even more significant.