One of the other possibilities that have been hinted at, at various points over the last few months, is that Affleck may very well be replaced in Matt Reeve's standalone film but continue to appear in other DCEU films, such as Suicide Squad 2 or Flashpoint.
This would be a terrible idea.
As much as some comic book fans may be excited about DC's apparent plan to dip their toes into their infamous 'elseworld' stories with Todd Phillips' upcoming Joker film, general audiences will be entirely confused by this.
The general public has a hard enough time as it is keeping up with the sprawling narratives of the multiple cinematic universes in play. Introducing the concept of two actors playing the same role but being completely unrelated will be hard enough with Joker but imagine for a moment a world in which the main DCEU films have Batman being played by two different leading men within the same story.
It is ludicrous. If Affleck bows out of the role now, it is a clear line in the sand and a single actor can continue to play Batman from this point forward, maintaining some semblance of coherency.