You could deal with them that way, sure. But every other person after them will learn not to divulge it and take the best offer from other countries (submission mentions offers from France and Pakistan for Phillips) and give it to them, because you're not going to reach a worldwide consensus on "let's get rid of every person that develops X theoretical doomsday device" and others will want that edge. This seems so shortsighted it'd do well together with the vitrum flexile story. Just like engineers after WWII, during and after the Cold War, you'd want to give them a comfortable position using their talent for something more productive than developing military-purposes missiles. I'd be more worried about biochemical warfare anyway, I'm surprised there hasn't been any major attack with water supply as a vector.