You think South Korea could absorb North Korea that easily?
South Korea isn’t West Germany, and North Korea is a nightmare compared to East Germany’s development.
Part of the reason China and Seoul aren’t eager for the regime to collapse is because millions of uneducated, starved peasants will flood into their countries.
Personally, I think North Korea would need a lot of foreign humanitarian aid.
I think they have very different reasons for fearing NK's collapse. Education isn't all that big a deal - these are pretty sharp people, who will improve tremendously with proper nutrition and instruction. NK is not a garden variety basket case country - notice that Zimbabwe doesn't have working nukes or ICBM's, and has to import its weaponry. For China, NK's fall will remove a buffer state, and bring US troops all the way to the Yalu river - something they fought a war in 1950 to prevent. For SK, NK's fall could bring about a Chinese intervention and an attempt to annex North Korea - which would bring about war with China and the Chinese confiscation of SK's plants in China as well as an interruption in its lucrative trade with China.
The backlash against Japan in the postwar era has distorted Korean views about Japan, but the principal threat to Korean independence for most of Korea's history has been China rather than Japan. If it weren't for Japan's annexation of Korea in 1895, Korea would probably be a Chinese province today.