Deathstroke Could Be An Even Bigger DCEU Villain After The Flash

screenrant.com:

While Joe Manganiello's Deathstroke won't fight Ben Affleck's Batman as originally planned, the multiversal events of The Flash could make him an even bigger villain in Batgirl's universe. Batman v Superman: Dawn of Justice introduced a seasoned Batman who had already gone through many struggles throughout the years. Yet, his world-saving missions with Superman and the Justice League were only the preamble for what almost became his biggest battle: The Batman, originally planned to star Ben Affleck as the Dark Knight, would have focused on a fight against Deathstroke so brutal that the villain would've killed one or more people close to Batman.

Plans changed, however, and The Batman, now starring Robert Pattinson as Bruce Wayne, will launch an entirely new franchise set in its own universe. With Ben Affleck making his last appearance as Batman in The Flash and Michael Keaton returning for Batgirl, it would seem like Joe Manganiello won't be able to reprise his role for a long time. However, the villain can still return to torment a different Batman than originally intended, and he could become even more ruthless while doing so.

Related: Why The Flash Goes To The Michael Keaton Batman Timeline

How the DCEU multiverse really works will only be made clear once The Flash releases, but casting choices for future movies have already teased the aftermath of the Flash's adventure through the multiverse (a la No Way Home). After his appearance in The Flash, Michael Keaton will return in Batgirl, which also includes J.K. Simmons in his second appearance as Commissioner Gordon after Zack Snyder's Justice League. This means that at least part of the universe that Ben Affleck's Batman inhabits will survive the events of The Flash.