Let's say that Pope Pius III manages to survive longer (or isn't poisoned by Petrucci--depending on which version you subscribe to), perhaps managing to live into his early seventies and reigning ten years or so. During this time, we'll assume he remains largely under the control of Cesare Borgia, who keeps his papal offices and remains in possession of the newly carved out duchy of Romagna (along with Valentinois, Urbino and his other territories). Now, we'll also say that Cesare lives a bit longer in this scenario, as remaining in Italy will ensure that he is not killed while in exile, fighting in Navarre.
So, taking all this account, in this scenario, Cesare manages to secure his rule over Romagna, sire a son with his Albret wife, and lives to fifty or so, dying around 1526. Obviously the butterflies are going to be massive, and it will take a bit of luck on Cesare's part, but then, I'm inclined to agree with Machiavelli that as long as he has the support of the papacy, his own political and military skills will do the rest for him.
What are the effects of this? I'm curious to hear everyone's thoughts here, as to my knowledge, the question has never been asked before...
Amitiés,
Endymion