And post-communist Russia is an example of what could happen in North Korea, replacing one group of tyrants with a mafia. Only N.K. doesn't have the kind of natural resources Russia has. Maybe Albania might be a better example.
So, when the communism collapsed in 1990, the country collapsed too. What saved the people was the fact that Albania is a very small country of 3 million in the middle of Europe so about 30% of people were able to immigrate. Now where would 8 million of North Koreans immigrate if suddenly communism collapsed in their country? I don't know.
Many would migrate to China, and this is probably one of the main reasons why China tries to keep the status quo in North Korea. China does not want a collapse of their neighbour.
Special Economic Zones are the name of the game, and yeah, it'd take decades to transform the whole economy -- China's still working on it. But the standard of living can start increasing almost immediately with the combination of trade and increased aid once they stop being an international pariah.
"Screwed" is on a spectrum, and you can start moving up immediately, if slowly.
There is only a handful of people that are in charge in North Korea that can try to effect some kind of change. But even if suddenly one day they wake up with the best of intentions and all cleared up about where they would want to go, i.e. to achieve some sort of South Korean democracy, it will be extremely hard to improve anything in a short amount time (and by short time I mean around 10 years).
Basically the people living there today are screwed. Ideologically they have grown up to expect everything handed down from the state. How can the state hand down everything if it doesn't own everything? Economically, maybe 90% of economic activity is useless. In a free economy all of them would be closed. How would you cope with 90% unemployment?