I'm not sure that's good for North Korea.
Sure it is. NK's goal is not to "get" Sony. It is to maintain the reputation of their leader as a psychopathic kook. This will strengthen their hand in future negotiations over important issues. If you act reasonable, your adversaries will insist on an outcome that is "fair". But if act like an irrational psychopath, your adversaries will settle for any outcome that is even halfway sane. The Kim dynasty has been using this strategy since 1950, and it has worked well for them.
Worked for Nixon.