Let's say a shadowy figure, like, say, a former high up spy happened to privately make the highly unofficial statement to someone high up along the lines of "Hiroshima, Nagasaki, Medina, Mecca."

Highly plausible deniability, and perhaps something very good might come from it. Like, the end of money being funneled to terrorists, the end of Wahabbi expansion, and a severe crackdown on extremists.

Mutually Assured Destruction worked for decades, and it would probably work again. However, you need a rational actor, such as the Saudis.