The DPRK has built up incredible resistance to economic warfare and is self-sufficient in several areas. The few areas where they are reliant on outside support, mainly oil, is currently a priority for the government and they're making great progress. The rolling blackouts in Pyongyang that were a staple of life post USSR collapse have mostly diminished, for example.

No one will deny that the DPRK and ROK both have powerful militaries. The ROK is more powerful on paper, but the DPRK has several advantages. They have one of the most disciplined armies in the world (which was already a key factor during the Korean war). The tunnel systems near the DMZ make Hamas and Hezbollah's tunnels look like child's play. There is universal arming and weapons training of the entire populace through the Worker-Peasant Red Guards and affiliated organizations, and the citizenry are highly ideologically motivated and educated. This means that if the DPRK government even were to collapse, the US would have to fight off an insurgency much larger and better organized than the one in Iraq. Not to mention that the ROK's economy and military is completely reliant on the US and an American pullout would lead to a rapid takeover. Oh, and the DPRK has nukes.