I think that's the whole point of the ship, it's mere existence deterring and forcing the enemy to reconsider it's actions, especially if it might be armed with nuclear warheads. I don't think DPRK has any unrealistic thoughts about these ship surviving for any significant length of time in a war, no one would, and i don't think it's the point. I think preventing such a war in the first place is the whole point, being another leg of the deterrence, and IF a war does happens, it will be just one of the retaliation enablers, either tying down enemy forces that otherwise would target other retaliation means, or surviving just enough to launch it's counterstrike. The enemy can't be in all places at once.