the problem with the situation in North Korea is the fact that there just aren't any viable military options. I didn't say that aren't any options―only that any pre-emptive use of military force will create intolerable consequences.
A regime change as you suggested is the preferable choice. Keep in mind though, that this is a leader whom the people view as deity and eternal― the only caveat being that he assassinated his own half-brother, Kim Jong Nam, and consequently, may have weakened his own claim to family immortality in the minds of his people.
There are many ways to carry out a regime change . Kim Jong-un has already provided one example by using assassins to carry out the murder of a family member. It's unlikely the Chinese would initiate or sanction the killing of Kim Jong-un though― the most that could be hoped for is quiet non-interference― and that too is unlikely.
A military coup is possible, but given the extreme indoctrination of the people and leadership, this again is highly unlikely. The most feasible scenario is a sleeper cell inside North Korea manned by Korean nationals who are prepared to mount a suicide attack against Kim Jong-un such as was used against Anwar Sadat, in Egypt in 1981.
In my opinion, there is no other viable option
Well others have suggested that some sort of Chinese action to do the same may be possible. One would presume that they have some sort of presence there.
perhaps, it's murky to say the least. I reserve the right to be wrong :)
I think being wrong in these matters is almost guaranteed! There probably is no absolutely correct answer or good solution - just a set of different wrongs. I'm just glad I don't have to make military decisions like this for any nation.