It's not the same situation and I think it's hard to believe it will ever be - it only on the surface seems to be similar because it involves two countries of different systems that are bonded by same culture, history and language up until the split. The details matter; the German unification was a result, as you may remember, of the Autumn of Nations revolution that lead to fall of the Eastern Bloc and Soviet Union; the situation was building up for over 10 years if not more - some consider the Chernobyl disaster as being the first domino piece that fell down, some the strikes and emergence of 'Solidarność' movement in Poland or even 1968' Prague Spring.
North Korea is alone on the playground and at best is being supported by People's Republic of China, economically and politically (to some degree); it holds power in a good grip, the propaganda machine and control of citizens life works there very well - at least from what we know. There's simply no possibility for opposition movements to exist and even be strong enough to question the Kims power and images as leaders. I'd rather expect that China would eventually incorporate North as another province rather than South deciding for the unification which certainly would have some harsh social and economical outcome. The differences between these countries seems to be too big to just dismantle DMZ and become one happy Korea with population of ~76mln.
Still, it's a wild guess and anything might happen.
North Koreans are very nationalistic and would never accept a Chinese annexation, and South Korea would very likely join the conflict against China annexing ethnically Korean populations and lands. Nothing like identity politics to rile up the population and topple some politicians.
It's far more likely that SK eventually ejects US military bases from their country and SK and NK work towards a loosening of borders and increased economic ties with Chinese acknowledgement but still wary of Chinese interference in the process. Especially considering the shifting power balance in Asia, having US military bases will eventually be more of a liability than a benefit for SK.
North Korea is alone on the playground and at best is being supported by People's Republic of China, economically and politically (to some degree); it holds power in a good grip, the propaganda machine and control of citizens life works there very well - at least from what we know. There's simply no possibility for opposition movements to exist and even be strong enough to question the Kims power and images as leaders. I'd rather expect that China would eventually incorporate North as another province rather than South deciding for the unification which certainly would have some harsh social and economical outcome. The differences between these countries seems to be too big to just dismantle DMZ and become one happy Korea with population of ~76mln.
Still, it's a wild guess and anything might happen.