Arrow Season 8 will get a new Deathstroke in its last season, though who it might be isn't clear at this time.
The synopsis for episode 4, "Present Tense," teases the appearance of a new Deathstroke and the return of Curtis Holt/Mister Terrific. There will also be a plotline regarding Team Arrow taking on John Diggle Jr./JJ in the future after a loss.
ARROW
“Present Tense” — (9:00-10:00 p.m. ET) (TV-14, LV) (HDTV)
ECHO KELLUM GUEST STARS – When a mysterious new Deathstroke appears in Star City, Oliver (Stephen Amell) and Team Arrow insist on taking down this villain themselves. Meanwhile reeling from the loss of one of their own, the future Team Arrow figures out a new way to try and stop JJ. Kristin Windell directed the episode written by Oscar Balderrama & Jeane Wong (#804). Original airdate 11/5/2019.
Played by Manu Bennett, Slade Wilson/Deathstroke is a key character in Arrow. Wilson served as a mentor to Oliver Queen before later becoming a major antagonist. Eventually, Wilson and Queen began working together again, though the latter hasn't appeared on the show since Season 6, though he was mentioned several times in Season 7.
In Arrow's future timeline, JJ -- the son of John Diggle, Jr. and Lyla Michaels -- becomes the leader of the Deathstroke Gang. The synopsis seems to indicate this new Deathstroke is not JJ, as he would still be a child in that timeline. The synopsis does not make clear if this episode will be taking place on an alternate Earth.
Airing Tuesdays at 9 p.m. ET/PT on The CW, Arrow's final season stars Stephen Amell as Oliver Queen, David Ramsey as John Diggle, Rick Gonzalez as Wild Dog, Juliana Harkavy as Black Canary, Katie Cassidy as Black Siren, Katherine McNamara as Mia Smoak, Joseph David-Jones as Connor Hawke and Ben Lewis as William Clayton-Queen.