I think it’s clear that Putin’s obsessive fear of illness or poisoning shows just how much he values his life and power. But I am sure that he’s not someone willing to go down without a fight, but his biggest fear of that is internal. That said, I’d argue that the dynamics of war, and especially nuclear war, are different today than they were in World War II, precisely because the threat of mutually assured destruction now acts as a deterrent, even for someone like Putin.
Regarding World War II, I wouldn't downplay the immense suffering caused by the atomic bombings of Hiroshima and Nagasaki. While it’s true that the war did not involve a nuclear attack against "one" of the combatants, the use of nuclear weapons on Japan was a game-changing moment that reshaped global diplomacy. It’s an important distinction, because of the horror of that chapter in history and the lasting impact it had upon the world in understanding that mutually assured destruction is a very real threat..