Imagine the timeline where Trump is finishing 8 years in the White House with North Korea having completely changed from a rogue nation to a fledgling democracy. Impeachment and a single term presidency is probably the more likely but it's been a funny few years in politics.
IIRC, North Korean diplomats apparently regularly ask if Trump is legitimately a madman or just pretending. Fighting crazy with crazy may actually be paying off.
Although I can't trust NK just yet. It wasn't that long ago that Kim had his uncle assassinated in an airport. Trump's shift of foreign policy has probably helped but I imagine the sanctions has had greater impact. Once they're relaxed, I'm sure NK would just revert back to being the rogue nation.