I would still rather have Saúl. Rodrigo is very like Busquets, and I totally understand why he'd be so appealing to Pep, but Saúl is the spiritual successor to Fernandinho. The complete midfielder who's played as a 6, box to box, a number 10, even RB, LB and CB when needed and done well. He also has the same never say die attitude, the engine and pace, a smart head tactically and the habit of showing up with a special performance on the big occasion.
He's supposedly got issues with Simeone's defend defend defend outlook and would be available.