Not so sure about that.
Cavani is no longer the one who has the fitness to be the support striker for a better talisman: Zlatan. At this stage of his career, Cavani prefers to play central, and leading the line. He's been decent in situation like last season where inconstant young players can't lead the line. However, he's not that great, nor that committed that we have to bend over for him, now that we have new option with Sancho and especially Ronaldo.
With someone as capable of finishing like Ronaldo, it's the other way around. You need to free up space, and serve up chance for him, as he's the best at put away those chances. He's the one to build the team around.
IMO, after signing Ronaldo, I wouldn't care less about letting Cavani leave. Ronaldo, Rashford, Greenwood, Sancho, Bruno, Pogba on the left, Martial, Amad, Elanga, even Lingard and Dan James are more than enough cover for those attacking position