~The NorK’s could cut it off at any time leaving you at their mercy when your economy is dependent on that supply~
Putin and ROK would easily move in from two fronts and kick some butt. Ukraine is by far more formidable opponent than the Norks and look what happens.
North Korea has the 4th largest army/military in the world. The Ukraine isn’t even close.
Why would Putin move against North Korea? Russia, China and North Korea are long time allies. This should be seen as, exactly as the other fellow mentioned, an attempt to make South Korea dependent on its enemies for their gas supply.