Batman was going to die in Zack Snyder's original 5 part plan for the DC Extended Universe. The DCEU is headed in a new direction, and most of Zack Snyder's plans for the characters after the events of Batman v Superman: Dawn of Justice, including a significant portion of Justice League, were abandoned after he was forced off the project and extensive reshoots were conducted by Joss Whedon.
Over time, details for Snyder's plan for Justice League have continued to leak, including a number of details for his plans beyond that first major team-up, and Screen Rant pieced together a good idea of Snyder's original plan for Justice League 2, and now, thanks to a comment on the Vero social media platform, we have confirmation of a significant portion of that plan: Batman was going to die.
This newest revelation isn't only confirmation of Batman's death, but also gives us a significant clue as to Snyder's plan for Justice League 2 as a whole. We'd already suggested Final Crisis would be a major influence on Justice League 2, and this newest confirmation gives us another main ingredient for that story. First, Snyder planned to include Darkseid in Justice League as set-up for Justice League 2. Second, the Anti-Life equation was supposed to be introduced in the ancient battle with Steppenwolf. Third, Batman was supposed to die, presumably with the Final Crisis iconography Ramesh De Silva posted to Vero, indicating Batman sacrificed himself against Darkseid.
This revelation doesn't merely shed light on the Snyder's original intent for the story, but also gives a fuller picture of what happened behind the scenes in the DCEU during Justice League's production. This is the version of the story Ben Affleck would have signed on to portray, meaning his solo Batman movie would have been created with this ending in mind for the caped crusader. Looking at the timeline of Ben Affleck's departure, it's very clear it lines up with the time during Justice League's production that Snyder was clashing with Warner Bros. prior to his exit. So it's more than likely Affleck's lack of commitment to the director's chair was directly related to the fact that his Batman script was significantly impacted by decisions such as removing Darkseid - and he specifically said he wouldn't direct if he didn't like the script.
Ultimately, Affleck stepped down, Snyder was forced out, Justice League bombed, and now Affleck's future with the character is in doubt as Matt Reeves is telling a story that has nothing to do with the role Affleck originally signed on for. Even if he did want to play Batman, it may not be an option since Reeves is expected to tell a story about a younger Batman, so Affleck's involvement would be limited to potential narrator or modern-day bookend at most. Regardless, with the DCEU's new direction and confusion surrounding the future of both Cavill and Affleck in question, we're not likely to see this moment on screen any time soon - if ever.