Rodrigo survived the poisoning due to the quick action and medical knowledge of Lucretia, who administers charcoal through a tube she puts in her father's mouth to his stomach. The charcoal gets there just in time to absorb most of the poison, in a series of scenes that are both medically and dramatically satisfying.
But things get even worse for the Borgias, as a new villain - a genius master strategist working for Caterina Sforza - unleashes a plan that puts a blade within inches of the necks of just about everyone in the family. This includes the slowly recovering Rodrigo, who is about to be killed by Cardinal Ascanio Sforza - up to now an uncomfortable more-or-less supporter of Rodrigo - when Cesare bursts into the room. Ascanio manages to put his blade away before Cesare can see it, but we have seen just how close Rodrigo again came to death. And, again, it's exciting to see this - and how everyone in the family were but a "blade's breath" from death as Cesare puts it - even though we know historically that everyone survived.
The blade signals a profound shift in the heft of Borgia enemies. The poison was della Rovere's show, and although he has no shortage in pious cunning, he has none of the massive strategic power Caterina Sforza, who has moved into first place as the anti-Borgia this season. Which means it should an appealing, exciting season indeed.
See also The Borgias Season 2 Sneak Preview
And see also The Borgias Sneak Preview Review ... The Borgias 1.5: Machiavellian Politics and Marriage ... The Borgias 1.6: Beds, Leg, Cannon ... Borgias Season One Concludes