The fate of Russia's original Rurik dynasty was sealed when Ivan IV (a.k.a. The Terrible), in a heated argument with his son and heir Ivan Ivanovich surrounding the fact that the elder Ivan had just beaten up the son's wife and caused her to miscarry their child (I know, right?), struck the tsarevich in a fit of blind rage with his scepter, causing a fatal head injury. Not only was this bizarre episode a personal tragedy, but with that, the only heir left for Ivan IV was his mentally handicapped younger son Feodor, who died childless, which in turn led to the Time Of Troubles, marked not only by famine and disease, but a chaotic series of civil wars, power struggles, and war with interfering foreign powers.
Now, let's say that Ivan Ivanovich survives this encounter with his father, and remains the heir and takes the throne as Tsar Ivan V upon Ivan Grozny's death. By most accounts, he was very similar in personality to his father, sharing similar sadistic and hedonistic tendencies, while also being as intelligent and well-read. But if he lived (and someday produced an heir himself), the Rurik dynasty may have remained stable, and while the famines and disease outbreaks of the early 17th century would still happen, the wars and power struggles are avoided. What happens from there?