As I rcall, there was a series of 6 notably corrupt popes just before the reformation. Their actions, such as the building of Saint Peters, set the stage for Luther. On the other hand, there were 2 men who, if elected or kept in office, might have changed the course of the church. One was Marco Balbo of Venice, known for his high character and scruples, who came within five votes of being confirmed as pope. However, the two main challengers united behind Giovanni Cibo, who became Innocent VIII. The other was Pius III, whose first act upon taking office was to declare he would reform the papacy. However, he died after holding office for 26 days. I think that is a record. Anyways, he was serious. I think if Pius III survives, then reform is likely, and the reformation may be stillbourne.
Another possibility is no sack of Rome. There are several ways this can happen, but I cannot remember the specifics. Something about the Pope's best general dying during a skirmish, and the German cannons almost not arriving. Anyway, this means that the papacy is not so much under the Hapsbugh's thumb, so he may Grant Henry VIII a divorce. That removes the formation of Anglicanism.