Oh, I would absolutely love to have Sonny back. Just like I would love to have Jack back. And yes, both of them, rather than Ava or Andre'.Freddie Smith left on his own , it was his decision, he had a few projects he wanted to do.
We can want a lot, doesn't mean the show will agree. The thing is, actors on contract have to be paid whether they are working or not, and usually are guaranteed x number of appearances a week, maybe 1-3. Well, Paul has been on contract, and very unused, no story per se, thus "model".
I really like the character, and the actor, but he was brought on under the previous team of writers, and the new team evidently could not come up with story for him.
That said, I think Freddie Smith (Sonny) felt that since Will was going to be killed off, it would be a good time for him to leave and do whatever it was he wanted to do. But I also feel that Sonny would not just have upped and left Arianna like that.