I don't think they have seen anything over the event horizon either. They can't make legitimate strategy that involves nuclear annihilation. The risk comes from the fanatics they are cultivating.

The solution will be the same thing that will prevent the USA from being successful in large scale invasion, domestic rebellion. There will not be enough soldiers to fight, there are people who will fight the fanatics to stop a launch. It's tenuous, but it's what's going to happen and when you consider the circumstances, it's the only way it can happen. The empire has to eat itself.