Whenever did sanctions work with totalitarian dictators ? As long as Jong-un can keep himself and his elité happy and most of the population alive and working then it probably doesn't matter to him. A failed and unfixable nuclear program does matter to him. I see the summit as a sign that he isn't getting the necessary help with his nuclear program from outsiders including China. So he has switched tracks to a unification narrative and the question is to which degree he will follow up on it. In the past he has gone back on pledges so only time will tell.