If it was up to media and fans to cast actors for movies, it would have been set at the very same day as Johnny Depp confirmed that he is leaving Fantastic Beasts 3, that Danish actor Mads Mikkelsen would replace him. The bad news is that it really isn't media and fans who get to decide this, but the good news is that Warner seems to agree that Mikkelsen would be perfect for the role.
Warner Bros has now officially confirmed that Mads Mikkelsen (known from movies like Casino Royale and Star Wars: Rogue One) will replace Johnny Depp in Fantastic Beasts 3, playing the evil mastermind Gellert Grindelwald. Fantastic Beasts 3 is currently being recorded and plans are to release it in the summer of 2022.
Other confirmed actors are Eddie Redmayne as the protagonist Newt Scamander and of course Jude Law as a very (very!) hunky Albus Dumbledore.