Prometheus may be dead, but the Arrowverse writers have found a way to bring the character back in the form "Prometheus-X," during the upcoming four-way crossover between The Flash, Arrow, Legends of Tomorrow, and Supergirl.
After fighting the immortal warrior Ra's Al Ghul in season 3 and the supernaturally powerful Damien Darhk in season 4, producers and writers of Arrow knew that it would be hard to find a main antagonist that could match the threat level of the last two villains. The answer to this problem was Prometheus, an enemy who could emotionally challenge Oliver like no one else before him. Using psychological warfare, Prometheus nearly broke Oliver. After being unmasked as district attorney Adrian Chase (Josh Segarra) most of his plans were eventually thwarted, but in the end, Prometheus still got what he wanted by committing suicide and possibly killing several of Oliver's friends.
EW has confirmed that an alternate universe version of the character, Prometheus-X, will appear in the upcoming Arrowverse crossover, "Crisis on Earth-X." EW also reports that "there are no plans" for Josh Segarra's return, meaning that Prometheus-X will never be unmasked, or that someone else is using the identity. EW theorizes that Prometheus-X will actually be the Earth-X counterpart of Quentin Lance (Paul Blackthorne), who was suspected to be Prometheus at an early point in season 5.
It was previously announced that "Crisis on Earth-X" would bring the heroes together for the wedding of Barry and Iris, only to have it interrupted by villains from another world. Known as Earth-X, this world exists as a much darker reality where the Nazis won World War II. Earth-X is the home of evil versions of the Arrowverse heroes, including Overgirl, Dark Arrow, and Dark Flash, who were all teased in promotional art for the crossover (see above). Also included in the artwork was the first hint of Prometheus-X's involvement, though at the time it wasn't clear if this could be a different archer. Fans will have to wait and see if the crossover will feature more alternate versions of Arrowverse villains.
"Crisis on Earth X" takes place across two nights on Monday, November 27 and Tuesday, November 28 on The CW. Supergirl and Arrow will air on Monday and The Flash and Legends of Tomorrow will air on Tuesday.