The Flash teaser suggests that Michael Keaton’s Batman will return for the first time since 1992’s Batman Returns. Although Bruce Wayne narrates the majority of the teaser, there isn’t always a single image of his face. This raises a lot of issues about who Bruce Wayne is now, all these years later.
There are also signs and indications that he hasn’t been visible in a long time, most likely because Batman faked his own death. The preview for Batman: The Flash makes it appear as if Bruce Wayne’s mansion, Wayne Manor, hasn’t been maintained in years. Tim Burton’s Batman flicks had a fantastic gothic look to them, but this film’s unit was very different.
After Batman Returns, Michael Keaton’s Batman should have faked his own death. The Dark Knight Rises ended with Christian Bale’s Bruce Wayne “dying” in the process of saving Gotham, but this was utilized to wrap up his story. It’s likely that Bruce will retire in some form, but there’s a chance that the reason will be due to Bruce faking his death. It might explain his lack of heroics in recent years and serve as an introduction to his story in The Flash. For The Flash, Michael Keaton’s Batman should have pretended to die.
That doesn’t explain why he appears in the movie, but it does explain why Barry Allen crosses paths with him. Ezra Miller’s Flash and Ben Affleck’s Batman have established a mentee-mentor combination in the Justice League. As soon as he adjusts the past and future, it may appear like Barry Allen seeks out Bruce Wayne.