Rowling defended the decision not to recast Grindelwald, stating: "Based on our understanding of the circumstances, the filmmakers and I are not only comfortable sticking with our original casting, but genuinely happy to have Johnny playing a major character in the movies." And Depp recently added, "J.K. has seen the evidence and therefore knows I was falsely accused" -- seemingly suggesting that he showed Rowling some sort of exonerating evidence, presumably on a piece of an enchanted parchment that no one else is allowed to see.
Harry Potter himself, Daniel Radcliffe, pointed out that this was kind of hypocritical. Back when they made Harry Potter movies that actually featured Harry Potter, the producers did fire someone for their offscreen actions. The bully Crabbe was written out of the final film after his actor was caught growing pot plants in his mom's house. As Radcliffe bluntly put it, "What Johnny has been accused of is much greater than that." Several Potterheads also took issue with Rowling's support of an alleged abuser when her books were literally about a kid escaping an abusive home. Hell, even Disney has reportedly dropped Depp from a planned Pirates Of The Caribbean reboot, and their theme parks are practically infested with animatronic Jack Sparrows.
To top it all off, Rowling already had an in-universe way to drop Depp like a box of unwanted scarves. Remember how Season 5 of House Of Cards ended? Robin Wright's Claire, now in the Oval Office, ghosts Kevin Spacey's Frank, then turns to the camera and says "My turn."
One might think that that Netflix cobbled that ending together with a CGI Spacey after he was accused of sexual assault. But this happened before he was fired from the show, perfectly teeing up the Spacey-less season. The producers fell ass-backwards into a solution to a problem they didn't have yet.
Similarly, Rowling had the perfect out, but chose not to take it. Depp was barely in the first Fantastic Beasts. His character spent 99 percent of the movie disguised as Percival Graves, played by Not Accused of Domestic Violence Actor Colin Farrell. It's only in the finale that Newt uses a spell to reveal Grindelwald in all his "Sad divorced dad at an Arcade Fire concert" glory.