Well, no, they probably wouldn't *kill* him. That's not how Richards rolls.
However, he might mention just how easy it would be, and then explain, "no, we won't kill you. However, if I was willing to effectively lobotomize my own son once so his powers wouldn't run amok, what do you want to bet that Sue here would be willing to give you a series of tiny strokes with her force fields? No, you won't be dead, but you'll be drooling in a wheelchair with no motor control or ability to speak. Best part, invisible force fields leave no forensic evidence."