Diablo was originally going to survive in Batman v Superman: Dawn of Justice and Suicide Squad. Despite adapting many fan-favorite characters from the comic books, Suicide Squad still had trouble connecting with audiences.
Suicide Squad put together a team of villains consisting of Harley Quinn, Deadshot, Killer Croc, Diablo, Captain Boomerang, and Slipknot, while also adapting Katana, Enchantress, and the Joker. The film heavily focused on Harley Quinn and Deadshot, while sidelining other characters like Joker and Slipknot, the latter of which was killed off at the very beginning of the mission. Diablo got the spotlight in the final act of the film when he sacrificed himself to destroy Incubus (the brother of Enchantress), but he wasn't originally supposed to die.
Suicide Squad director David Ayer recently responded to a fan asking about Diablo's fate in Ayer's original script. Ayer confirmed that Diablo was going to survive, but his death was added in during reshoots. Ayer's original tweet can be read below:
In the years since Suicide Squad's release, fans have been made aware of the Justice League still hasn't seen the light of day.
The DCEU has improved with both fans and critics since 2016, with Warner Bros. giving more creative control to directors and focusing on ion projects rather than building an extended universe. Fans are no doubt hoping that the studio gives James Gunn full creative control of characters from Suicide Squad are returning for Gunn's film, but Diablo more than likely won't appear since he was killed off in the first film.
Source: David Ayer