What happens after North Korean regime's Collapse?

  We all know the North Korean regime has been shaky, like a tooth that is falling out.
But the question is: What's Next?

   First of all, what is sure is that there will be massive refugees flowing into South Korea and China.
The Political aspect may be more complex, and has several possibilities:
1. Since the "Western block" led by USA and "Eastern block", mainly China and Russia may still have the intension to expand and control the geo-politics, there may be a conflict over the land with no lord.
2. A more peaceful alternative of 1. which is by negotiation along with South Korea and Japan, but who is going to be the future leader and what type of regime will take control is uncertain.
3. Reunification by peaceful means. With substantial aid and reconstruction, the new country - Korea will be based on Democracy and Peace. This is the most hopeful and best situation, and indeed not impossible, like East and West Germany also unified ultimately.