Good article about how Sanditon came back, and about Theo James not returning.
“He never signed an option, so he was never obliged to come back, but we had talked about it. But I think he genuinely believed that it was an interesting ending – he’s a creative. So that’s the fundamental reason why [he didn’t return] and he was busy with other work,” said Campbell, who’s also the head of Drama at Red Planet (the production company behind the show).
https://nypost.com/2022/03/11/how-steamy-jane-austen-show-sanditon-got-un-cancelled/