Apparently free from his stone prison, Sorin was lured to Ravnica by the Interplanar Beacon, and immediately became trapped there due to Bolas's use of the Immortal Sun. (It is unknown how Sorin freed himself; the Beacon itself may have pulled him to Ravnica, or at least provided enough of a focus for him to concentrate on something other than his pain.)
When he found out that Nahiri was on the plane as well, he immediately went after her, as not even a threat to the entire Multiverse could persuade them to put aside their feud. Ignoring the battle that raged around them, the two planeswalkers fought each other in single combat.
However, they later came to a temporary truce, joining forces against the Eternals of Bolas' Dreadhorde. They were among the few planeswalkers who chose to remain on Ravnica after Chandra disabled the Immortal Sun, helping the Gatewatch in their fight against Bolas.
It is unknown what happened to Sorin and Nahiri after that, although it has been confirmed that they both survived, and it can be assumed that they'll resume their feud.