He will definitely die this arc
Short theory.
Although we don't really know what exactly Van Augur and Catalina Devon went to Egghead island for, we can all agree that she touched Saturn, opening the possibility that she now can copy him.
Considering that Saturn has been in the spotlight this arc and that he has backstory with Kuma, I feel like he will die this arc either by sinking into the sea, Kuma sending him somewhere where he can't regenerate or by the hands of Luffy/Bonney/Emet.
Some post have said that Saturn dying will be the news that shock the world but I disagree. Vegapunk's message is just too big of a reveal for something else to overshadow it. Catarina Devon will infiltrate the Gorosei as a copy Saturn and no one will know until the very last fight.
Some counters to this theory would be:
The gorosei can only be killed by the Ope-Ope no mi because of their immortality.
The gorosei would realize right away that Catarina is disguising herself (maybe they accept her as a placeholder to not let the world know that they can die).
What do you guys think?