Sorry, I just saw this!
I don’t know, honestly. I think the initial plan was for Pedro Luis to take power in Spain, Cesare to follow Rodrigo as cardinal and eventually Pope (l o l), and Juan to carve out a Borgia territory in Italy, but Pedro Luis’ premature death followed by Juan’s murder wrecked it, and the possibilities inherent in Louis’ various problems/releasing Cesare to marriage and war changed everything.
So, retracing things a bit, if Juan was still alive he’d still be gonfaloniere, he’d still be failboating around, he’d still be antagonizing everyone
and their dogs. Cesare’s still a cardinal, his talents wasted on petty administration and supporting the Pope. Juan was already married, so the possibility of Carlotta would… not be relevant for him.
*thinks it over*
It’s possible that Cesare might have been released from his vows even with Juan alive to marry Carlotta (or, in the event, Charlotte d’Albret or Germaine de Foix). But I think Alexander, who was not a particularly adaptable man, would have been extremely loath to give up his original plan with even less halting it. IMO Cesare could not have gotten away with renouncing his cardinalship if Alexander had not been onboard; as it was, the cardinals essentially handed over the decision to the Pope. Now, warrior-priests were certainly not unknown irl (hey, Carrillo, hey, della Rovere), so it’s not impossible that Cesare could still have had a military-political career of some kind.
I can’t think it’d have been anything on the scale of his RL one, when all Alexander’s hopes rested on him and he had a tremendous amount of freedom to do whatever he wanted. Given that we’re only looking at five years of time—yeah, I think in the best case scenario it’d have been more limited.
That said, I do find the possibility of Cesare being a cardinal at his father’s death intensely interesting. In some ways, despite being much more hemmed-in through those five years, I think he would have been less vulnerable? It would be Juan who’d lose everything, assuming nobody else killed him yet—it might even be Juan with the malaria attack. And the sheer amount of trouble Cesare could have caused in the College of Cardinals is kind of a glorious prospect, lol.