Would it be more likely for the north to become an autonomous region of China rather than join with the south? I can't see there being any sort of joint sovereignty (unless duly elected of course)
I don't think (and I don't believe any experts think) that the North would ever willingly lose soverignty. I don't see it agreeing to be an autonomous part of China or Russia (the only allies it has), and joining with the South would definitely be out of the question!
I think it is almost unanimously believed by experts in the field that one day the regime will be toppled. The question is when.
In 2010, with Kim Jong Il's health deteriorating, his successor Kim Jong Eun being relatively unknown inside the country, currency revaluation problems, and whispers or restlessness and discontent coming from inside. Kim Jong Eun has now been promoted and much work appears to have gone into building him a reputation, currency problems appear to have improved, etc. resulting in the regime appearing stronger.
Whispers from insiders still show the discontent and growing impatience of the population, including, I understand, the middle-class businessmen. It is a country with great security over its population and little internal communication so it will be hard to co-ordinate much action, but when people have nothing except empty stomachs and they understand this, it's amazing what could be done at the right time.