Demento,
  1. My solution is to continue the sanctions in place and make it abundantly clear that any use of nuclear weapons on their part will result in a massive retaliation that would end life on the N. Korean peninsula. Naturally, any conventional military assault on S. Korea or any other nation by N. Korea would also come with a swift and measured response; 2. You clearly misread my post as I made it clear that N. Korea would regard any evacuation of Norther cities in S. Korea to be an aggressive precursor to the resumption of hostilities and would force N. Korea to attack immediately. That means that any attempt to evacuate these cities would result in mass casualties and war; 3. China may not support N. Korea in the war directly, but might indirectly. It is highly unlikely that N. Korea would ever support the US in a war against N. Korea. N. Korea is useful for their interests and as a buffer state. And again, any evacuation would be treated as a precursor to war.