That said, if re-unification, happens I imagine the progress in the North will be rapid, and the country as a whole will become an even stronger regional power.
North Korea has no industry and the population has no education. The unification will be between a high-tech 21st century developed country and the middle ages. The first thing they will have to do is take over the schools so that the next generation in 15 years has a chance to build this country.
GDP 1990 West Germany in 1990 $24,485 East Germany in 1990 $10,430 (I'm not so sure about these figures but the direction is right)
For the most part, what I'm imagining is mass migration from the North to the South.
South Korea is a prosperous country that has developed in a relatively short amount of time but North Koreans don't have the education or skill to compete in a South Korean economy.
In a sense it's being tested right now in the Kaesong industrial area on the border. It gives the benefits of cheap labor, without having to use the Chinese.