This kinda worries me. I'd wonder what kind of a person the heir apparant is, it could be possible that hes more nuts than the father. Although I think if the military takes over they won't invade South Korea, its an extremely bad tactical move. First of all they'd have to get accross the DMZ then they'd have to deal with international reprocussions too.
It'd be stupid and never succeed, the problem is apparently a lot of the senior military officials are quite literally insane and delusional - much like Kim Jong Il himself.