That reason would be awful, and most likely the consequences too, but it's not readily obvious to me that the timing would be.
The North marching South would get little to no support from their allies and would be repelled rapidly before returning to the current status quo.
So yes, I am sure. Neither sides allies have any desire to be the agressor. Not to mention that simply starting a war to cling on to power might be the stupidest reason there is to start a war.
What if they didn't do that (at first), but instead (as an intermediate step) annexed the north as a colony with its own economy but South Korean governorship; and then opened said colony to worldwide foreign aid?
This would be very similar to the short-term arrangement negotiated between West Germany and East Germany after the fall of the Berlin wall. For analogous reasons, West Germany didn't want to immediately absorb/unify with East Germany; instead, they held political and military stewardship over East Germany until it could be built back up.
By a curious geographical coincidence, neither North Korea nor North China nor North Post-USSR are known for their independent reality-based reporting and I take it as a given that North Korea would never start a war of aggression. If the North should ever march South (again) it will of course be as a completely righteous response against intolerable provocation and aggression from its eternal enemy, as confirmed by media duly approved by Moscow and Beijing.
They're looking more ready and eager to do that by the month, and with the present Global political situation, the respect for current status quo seems to be at a low.
