I don't think you know very much about North Korea if you think that it's possible for the people to revolt (google their electricity situation and google their caste system) or for the regime to 'fix' itself and open itself up to the world. China was never able to block all outside information in the same way that NK does.

Bottom line is these people will continue to be held hostage if we do nothing - They've no access to information other than what someone might find on a USB that a tourist drops, and they've no means of forming a resistance due to the caste system and the other institutionalised ways of repressing 'subversive' action/thought.

Yes, there will be refugees. "Oh, these people we freed are free now", that's how it works. The global community can, like it did with the Syrian refugees, negotiate amongst themselves about who'll take how many. We have lots of global humanitarian mechanism in place to ease that process as well.

It's not like there'd be some power-vacuum that a new dictator would take advantage of either, you'd have a united Korean state. This United Korea would absolutely make it a priority that the NK refugees are helped and settled into their cities.