Any reason to assume his replacement (another Kim family member, military junta) will be an improvement?
My impression is that the regime depends on the cult of personality built around the Kim family. Taking down Kim Jong Un would destabilize the regime. The question is how -- I think driving him crazy is the best solution; at some point (one hopes) the people around him will have had enough and take him out on their own.
The wild card is li'l Kim's sister, Kim Yo-jong, who's said to be NK's head of propaganda and agitation. I don't know that the North Koreans would accept a female cult leader, but if anybody could do it, she could.
As to the possibilities of a military junta, I think their influence would last only about as long as the food -- not long. They don't have the cult-like status of the boy king.