Launch back.
They're willing to kill you just for power. What makes you think they won't kill others in their struggle? At least you're struggling with the deciison. When you nuke their asses, you feel bad, and you wouldn't want to nuke anyone else. Other countries will respect that, and if they decide to attack you, then they'll remember what you did.
Remember World War 2? Japan attacked first, so we retaliated with a horrifying atomic strike. The terrorists repeat, and we go over there to kill them.
tl;dr You don't mess with the guy who's hated by everyone.