Arrow: Why Manu Bennett's Deathstroke Left The Arrowverse
Many fans of Arrow feel that Slade Wilson, aka Deathstroke, was the best villain that the series had across its eight seasons, yet he is unlikely to make any further appearances in the Arrowverse. This is due to a combination of behind-the-scenes drama and the difficulty in continuing his story among the current crop of Arrowverse shows.
Slade's introduction into Arrow was something of a happy accident, with writer-producer Geoff Johns (who co-wrote the pilot of Arrow) suggesting they stick a Deathstroke mask with an arrow through the eyehole on the beach of Lian Yu to add visual interest to the first scene of Oliver Queen being rescued. When the show was picked up for a full first season, this left the showrunners having to figure out how to bring Deathstroke into the show. Enter New Zealand actor Manu Bennett, who played Slade Wilson as a member of the Australian Secret Intelligence Service (ASIS) who was also shipwrecked on Lian Yu while trying to rescue an exiled Chinese military commander. (In the comics, Slade was a lieutenant colonel in the US Army, before he became a mercenary.) Wilson acted as a mentor and combat coach to Oliver Queen until he was driven mad by a dose of the superdrug Mirakuru.
Feeling betrayed by his student even before Queen put one of his eyes out with an arrow, Wilson swore that he would destroy everything and everyone Oliver Queen loved and leave him begging for death before finally taking his right eye and his life. Slade was imprisoned in an ARGUS facility set-up on Lian Yu in Arrow's Season 2 finale, still swearing revenge despite having the Mirakuru purged from his system. He appeared once again in the Season 3 episode "The Return," when Oliver took his sister Thea to Lian Yu as part of her vigilante training, only for the two to have to fight Deathstroke after he escaped from his cell. Manu Bennett was dissatisfied with the writing on the episode, believing it ridiculous that Slade would have a hard time fighting both Oliver and the relatively green Thea Queen after everything he had accomplished in the first two seasons. As a result, Bennett swore that he was done playing the Arrowverse's Deathstroke.
Arrow faced another obstacle beyond Bennett being unwilling to return after Season 3; Warner Bros. old policy of having only one live-action incarnation of its DC Comics properties in film or television. At the time, plans were afoot to bring Deathstroke into the DCEU, with Joe Manganiello playing the film version of Slade Wilson. This same policy forced Arrow's showrunners to abandon their plans to utilize the Suicide Squad as part of John Diggle's on-going storyline, killing off the Arrowverse versions of Deadshot and Amanda Waller.
Thankfully, Arrow executive producer Marc Guggenheim was able to persuade the higher-ups at Warner Bros. to make an exception for Arrow's Season 5 finale, where a remorseful Slade Wilson joined with Oliver Queen to save his family and friends from the villain Prometheus. Manu Bennett was persuaded to return for the episode and returned once again for a two-part storyline in Arrow Season 6, where Oliver repaid the debt he thought he owed Slade by traveling with him as he searched for his estranged son. The two-parter ended with the former enemies making peace and Slade Wilson continuing his quest alone. While there were hopes this might lead to a Deathstroke spin-off show for Bennett, it was agreed by most that the episodes gave his character arc closure, if Bennett never played Deathstroke again.
As of Fall 2020, Warner Bros. still seems committed to reserving Slade Wilson for the DCEU, despite Deathstroke (played by Esai Morales) having been the main villain of Titans Season 2. Beyond that, with Arrow having come to a close, there is no easy way to bring the more heroic version of Slade Wilson back into action in one of the existing series. Even then, there is the question of whether or not Manu Bennett would be willing and available to play the role again. With all of these factors to consider, it seems unlikely that Arrow's Deathstroke will ever appear again elsewhere in the Arrowverse.