As GW said, they did have a son in 1509. John. Died like 3 hours after birth.
His survival leads to many immediate questions. For example, would Germaine be regent? She's French and a woman after all, none of which were ever traditional rulers in Aragon. She would need the support of somebody. And how would be this John III? Even if he gets to the adult age, that not automatically means he would be a good king. After all, Ferdinand was pushing 60 when he was conceived, so there is not a small possibility the kid would have autism or other mental problems.
Next questions would be how does Aragon reacts to the Comuneros revolt in Castile. Does it stay out completely, supports Charles, the rebels, or tries to free Joan and tries to puppetize her? The latter is something worth of Ferdinand - pity he's gone though.
And then there is the French/Imperial conflict over Milan. Common sense dictates a pro-Imperial stance, since a French victory is most likely just a first stone on the way of a French (re)invasion of Italy, which of course is bad for Aragon. OTOH, if Aragon does not have good relations with Charles, it might just stay out.
And finally as I pointed out in Gonzaga's thread, let's not forget the Ottoman threat, which is going to dictate a hughe part of Aragon's foreign policy.
Saturn said:
Although mostly because I can see fitting in with my own TL.
It would lead to a smaller "Spain" and one with less presence in the new world.
Not really. The American policy was a Castilian affair from the beginning. Ferdinand didn't even care about Columbus or the colonies when they were founded.
Maybe the Basques would even retain their own country.
Ups. My anachronism-sense just tingled.
3 Basque provinces have been Castilian for 3 centuries. And their inhabitants don't think themselves as anything else.
Navarre meanwhile has been invaded by Ferdinand in 1512. IOTL he handed the crown to his daughter Joan (in name only, of course) and therefore paved the way to full Castilian annexation in 1515. But would he do the same if he had a child? Navarre has a history of sharing kings with Aragon from time to time - maybe he decides to proclaim his son king of Navarre instead, as a previous step to him being king of Aragon. But then that would mean the Narrese rebellions spurred/supported by France IOTL from 1516 to 1530 that resulted in the division between French Navarre to the north and Spanish Navarre to the south would be a source of conflict between France and Aragon only instead. Damn.
So going back again, let's sort first if Aragon follows an Imperial alligned policy or a French alligned one. That's vital to figure how everything else to come turns out.