IMHO the only option is to accept the fact of NK as a nuclear power. The regime almost certainly has no intention of committing suicide, it wants to survive. It has seen that the world lives with India, Pakistan and Israel as nuclear powers. It has seen that Iran gets respectful handling when it makes vague motions in the direction of nuclear weapons. It knows that it's Game Over if it ever started a war. It knows that China doesn't want it to collapse, nor does China want a US ally right on its border.
Ultimately, the only thing to do it nothing, because there's nothing useful to do. Any country that wants nuclear weapons can get them, if it's suitably determined and prepared to spend the very large amounts of money.