Best case scenario. Hitler takes Moscow, which leads to a coup, with Khrushchev replacing Stalin.
I believe Khrushchev would have taken a much different course, basically abandoning Bolshevism, at least for the duration of the war, to unite the people, and ultimately defeating the Nazis. But certainly, the Soviet Union would have been a much different place after the war.
Yes, it would, and a more humane one as well without Stalin, just as China became less inhumane after Mao‘s death and the ousting of the Gang of Four from power.
To this day, I believe that Nazi Germany would have had reforms after the bloodhound‘s death, though there might have been an interlude, a power struggle between the top Nazis. As there was with the Gang of Four and the reformers under Hua Guo-Feng.
Maybe Heydrich, had he not been assassinated, could have become the new man at the top. He was, in his way, an opportunist, and while he was evil, he was not stupid.