You are probably right about internal threats.
I don't think it's a given that all out war would commence. The only war footing the North could sustain would be nuclear, anyway, and it's hard to imagine anyone coming to power there with a strong incentive to attempt that sort of campaign.
I think we'd just as likely pivot to a new set of actors and a new and possibly more unstable nuclear stand-off.
I feel very worried for the people of the DPRK under the circumstances.
I don't think the US has any pretext for preemptive military action against Kim Jong-Un at this point, but I'm sure there are a lot of hawkish and excitable DoD senior management with enormous budgets to justify.