I posted a few weeks ago that production on the second season of Atlantis was underway, and while the official announcement did not mention Sid, I assumed that was simply because they weren’t filming scenes with King Minos yet. I’ve since learned that Sid is not, in fact, returning for season 2.
Despite “a terrific cast and hardworking crew,” Sid told me that he was unhappy with the creative direction for his character and encouraged them to kill him off during the poisoning storyline toward the end of season 1. When King Minos recovered from being poisoned, Sid was surprised but declined to return to the show. It remains to be seen how the writers will handle his absence.