What if Joseph Stalin died on June 22, 1941, the first day of Operation Barbarossa (and before anyone asks if he gets assassinated, let's assume he dies from a heart attack or stroke caused by the shock of learning that Hitler had indeed betrayed him and attacked the USSR)? What happens next with Stalin dead on the first day of the Great Patriotic War? Who succeeds him as leader of the USSR after his sudden death? How does this affect the Soviet war effort?