They don't have any hostages......yet.
How many bombs do you think N. Korea has? Do you think they have the means to deliver a bomb like the one they just tested? I don't think so. I read weeks ago that the N. Koreans had enough fissionable material to make four or five bombs.
The U.S. military is already there and they can stop anything the N. Koreans have till the UN forces get there.
PS - I just suggest this as a possibility, none of this will happen. N. Korea and the U.N. will natter at each other for the next year or so. Too bad, It could be nipped in the bud.