China has borders with the following countries:
Mongolia, Russia, North Korea, Vietnam, Laos, Myanmar, Bhutan, Nepal, India, Afghanistan, Tajikistan, Kyrgyzstan, Kazakhstan, South Korea, Macao.
And I don't know enough about Asian politics except that in the NGE universe Russia is probably one of the big winners of second impact.
According to a report by North Korea's Public Security Ministry, the North estimates its losses from 2.5 million to 3 million people, about 12 percent of its population in 2009, from 1995 to March 1998.
North Korea has not yet resumed its food self-sufficiency and relies on external food aid from China, Japan, South Korea and the United States. In 2002, North Korea requested that food supplies no longer be delivered. (Woo-Cummings, 2002)
In the mid-2000s, the World Food Program reported that famine conditions were in imminent danger of returning to North Korea, and the government was reported to have mobilized millions of city-dwellers to help rice farmers.
Yeah, I think North Korea would do really well on it's own.