Zack Snyder's Justice League helped foreshadow the death of Ben Affleck's Batman that would be teased in Justice League 2 before happening in Justice League 3. The Snyder Cut has gotten its due as the four-hour film got released on HBO Max after fans had to wait years to see what the director had intentionally planned to do. However, that was only the opening for Snyder's trilogy as he had stories lined out for Justice League 2 and Justice League 3. Had the Justice League sequels been greenlit, the Knightmare future would have been fully executed in the follow-ups ever since the setup in Batman v Superman: Dawn of Justice. A big part of that storyline would have been the heroic and tragic death of Batman.
While Warner Bros. isn't planning on continuing the Snyderverse, the Dark Knight's fate in the sequels have been revealed through Snyder's concept ideas that have become public. However, the Snyder Cut helped kick off Bruce's destined fate through the conversation that Bruce has with Jared Leto's Joker in the final Knightmare scene. As the two rivals have an intense conversation, Joker says something that alludes to Batman's death being a key component to undoing this dark future. Joker states, "I often wonder, how many alternate timelines do you destroy the world because, frankly, you don't have the cojones to die yourself," foreshadowing that because Bruce wasn't willing to die, that's why they are stuck with this reality.
Justice League 2 would have ended with Darkseid killing Lois Lane and getting Superman to succumb to the Anti-Life Equation which sets off the Knightmare saga. The final scene of the unproduced sequel would have taken place five years into the future where Batman and Earth's remaining heroes would still be standing. In Justice League 3, The Flash would successfully have gone back in time to tell Batman a key sentence that would change everything. Bruce, who in that timeline was suspicious of Lois's lies about her pregnancy, would learn from Barry that he was right: Bruce was indeed the father. When Lois then shows up after Flash vanishes, Bruce does what he didn't do originally and listens to what she has to say about her information on Lex Luthor's plans.
This ties back to the moment with Joker in the Snyder Cut because Batman ends up saving Lois from being killed by Darkseid as he takes the hit from the Omega Beam instead. Because Bruce chooses to listen to Lois instead of dismissing her after she lied about their baby's biological father in Justice League 2, that changes the outcome in Justice League 3. By preventing Lois's death, Batman's sacrifice would lead to the team and the whole DC Universe to taking on Darkseid once and for all where they win. In the finale showdown, Batman, who was already dying due to being hit by Darkseid's Omega Beam, would sacrifice himself to take down the Apokolips lord forever.
That's why Joker's statement to Bruce in the Snyder Cut is more important than some may realize as it would be instrumental for Justice League 2 and Justice League 3. While it would have certainly been emotional to see Batman die on the big-screen, it would have been something new for the character's media history. Additionally, Bruce taking the hit to save Lois and preventing Superman from being corrupted by Darkseid is a huge way for the Caped Crusader to go out on. While Justice League 2 and Justice League 3 are, for now, not happening, the moment with Joker in Zack Snyder's Justice League began what would have been a heroic ending for Ben Affleck's Batman.
