I read a good one a while ago.

The USA leaves South Korea and takes its' 25,000 troops home.

NK would then be more isolated in a real fashion than anything up to the present time. In one move the USA would remove the Norths' reason for developing strategic weapons, the "fig leaf" of survivalist justification would be gone.

The North only has half the population and a tiny fraction of the Souths' economy and dynamism, it simply would/could not take it over.

And in a conventional war (which the South would never start) the North would be overwhelmed.

It would even vex the PRC, as they would be stymied in the games they are currently playing by continuing to support the North...

You may still see Japan exploring the possibility of nuclear weapons, and that as well would cause the PRC to pull its' hair out...for overplaying its' hand on the Korean peninsula...and while not the best situation, the acquisition of atomic weapons by Japan may be unpreventable owing to NK's move.