I guess that means SK is safe for a short while, at least until the new guys get comfy.
I would not assume this means SK is safe in the short term. According to the Chosun Ilbo article TLR posted over the weekend, it looks like Jang Sun-taek’s faction may be part of this targeted purge. I seriously doubt Jang (widely considered to be the #2 guy in the DPRK until Jong-un came on the scene) is going to go quietly.
This purge may very well invite (as AU72 suggested) a coup attempt (and serious one at that if led by Jang). A serious leadership struggle could lead the Kims to make a decision that the only way to preserve the regime is an external crisis.
At this stage, it won’t take much of a provocation to set the ROK off. A general resumption of hostilities (or even a “limited war”) on the peninsula could serve as that crisis.
If a purge goes smoothely, then I would agree that it may be pretty quiet in the short term while the new “young” generals loyal to Kim Jong-un solidify their positions. But if the stability of the regime becomes an issue, I believe it makes renewed hositilies more, not less, likely.