If the US, S. Korea, Japan and most other major powers just cut North Korea off completely it would just wither away and die.
China won't be able to send NK enough to save it.
We should pretty much just ignore North Korea. Monitoring their shipping to make sure they don't sell WMD and missiles, but other than that we should just cut em' off completely and ignore them. That means NO MORE humanitarian aid of any kind. No more heating oil, no more food aid, no more fertilizer. Just cut em' off and let em' rot away.