Consider that at the time he was the heir apparent. I doubt anyone would've dared touch him at that time.
Ordinary North Koreans wouldn't hear about this unless the North Korean government allows it to be published, so as long as he doesn't go around doing stuff that cause direct domestic problems for the regime, the only reason they'd have for going after him or his son at this point would be a personal vendetta.
If they were to go back and start walking around Pyongyang criticizing the regime to ordinary people or otherwise engaging stirring up domestic trouble, sure.
Ordinary North Koreans wouldn't hear about this unless the North Korean government allows it to be published, so as long as he doesn't go around doing stuff that cause direct domestic problems for the regime, the only reason they'd have for going after him or his son at this point would be a personal vendetta.
If they were to go back and start walking around Pyongyang criticizing the regime to ordinary people or otherwise engaging stirring up domestic trouble, sure.