During the history of the Soviet Union, change of the leader quite often resulted significant changes in the country. This is also when the leader simply died from the old age (J. Stalin, L.Brezhnev).
It is not very clear, why. Theoretically kings and dictators should not matter much in the history and be replaceable, if not him then somebody else. It must be strong social forces behind every dictator: he though he is leading them, actually they just pushed him in front of themselves.
But this view contradicts the experience, or maybe death of the current leader initiates changes that are long mature.