Renewal on the show seems very likely, but has not yet been formalized. Fans, though, should likely not take that as a bad sign: The CW does not yet appear prepared to officially announce renewals for any of its shows, with even seemingly-guaranteed renewals like The Flash and Riverdale. The network is developing a number of new projects for next season, so it may wait until it has evaluated those pilots to make official announcements for specific programming decisions.
Ryan will make a guest appearance on tonight's episode of Legends of Tomorrow, titled "Necromancing the Stone," and will return again in three weeks for the season finale.
Ryan, who originated the role of John Constantine in the short-lived NBC series Constantine, will star in an animated Constantine series for CW Seed launching on Saturday.
Constantine first joined the shared universe of The CW's DC shows with an episode of Arrow. At that point, Legends of Tomorrow had not yet launched and Sara Lance (Caity Lotz) had been dead for some time. After her sister Laurel (Katie Cassidy) used a Lazarus Pit to revive her, Oliver Queen (Stephen Amell) contacted John Constantine to help her be reunited with her soul.
Constantine helped save Sara, who would go on to join the Legends and is currently serving as the captain of the Waverider. In his previous appearance, Constantine and Sara teamed up in an effort to save a young girl possessed by a demon -- but the demon turned out to be Mallus, this season's big bad, and the girl turned out to be a teenaged Nora Darhk (Courtney Ford). Along the way, Sara ended up forming a bond with Mallus, which will come into play in a big way tonight.
A small group of dedicated fans lobbied for Constantine to return from cancellation for a long time after it ended on NBC. Before Ryan's character came to Arrow, there were even brief negotiations to bring the show over to The CW, but they fell through. Ultimately, once he joined the "Arrowverse," most of the most ardent Constantine backers felt that the way to go was to get him on Legends of Tomorrow, where Constantine seemed like a good fit for a ship full of misfit superheroes and antiheroes.
Expect more news on Ryan's role, and an official renewal for season 4, soon.
DC's Legends of Tomorrow airs on Monday nights at 8 p.m. ET/PT on The CW.