"By whatever means NK attacks another nation with a nuke, it will be the last thing they ever do."
Like a lot of people with little to lose (in this case partly because of sanctions) and who are pushed into a corner, and like people who refuse to be intimidated, I think NK is immune to that type of thinking.
 NK doesn't have a lot beyond their pride in their military and their ability to withstand and defy any outside pressure. Between death and submission, I think that NK is already resolved in its choice, and may pull a Samson involving SK, and the USA forces in the region before it allows the USA to think it has won over them. 
Maybe NK can't currently launch a nuke, but I read on Wikipedia:
"The Hwasong-10 is a North Korean designed intermediate-range ballistic missile with range capabilities of up to 1,550 miles (2,490 km), and could carry a nuclear warhead."