Despite rumors and murmurings that actress Amber Heard would not be returning for Aquaman 2, it would seem Heard herself disagrees. In a recent interview she stated: "I'm super excited about the amount of fan love and the amount of fan appreciation that Aquaman has acquired and that it has garnered so much excitement for Aquaman and Mera that it means we'll be coming back." While some had suggested that Warner Bros. may have been interested in re-casting the role or dropping it entirely, it would seem there are no such plans in place at the moment.
While the film is not technically greenlit yet, Heard says production is planned to begin in early 2021, and as one of the few unqualified success stories of the DC Cinematic Universe, a sequel seems all but inevitable. The particular controversy over Heard, however, likely has more to do with public controversy over her relationship with Johnny Depp, her ex-husband.
It's a long, complicated, messy story, but the summary is this: Heard publicly accused Depp of abusing her during their troubled marriage. Several tabloids, including The Sun, ran with the story. Further information came to light that muddied the waters significantly, revealing situations in which Heard had acted abusively. Depp then went on to file multiple lawsuits against various entities for libel and defamation, one of which he lost against The Sun. Depp was then asked to leave Fantastic Beasts 3, likely due to a mix of PR concerns and being caught up in several court cases that conflicted with shooting. As a result there has been some backlash from those who feel Depp was wronged, and are upset that he was asked to step down from his project, while Warner Bros. was still employing Heard on Zack Snyder's Justice League and presumably Aquaman 2.
Heard herself seems unbothered by the whisperings: "Paid rumors and paid campaigns on social media don't dictate [casting decisions] because they have no basis in reality. Only the fans actually made Aquaman and Aquaman 2 happen. I'm excited to get started next year." It would seem there are no plans to reduce Heard's involvement in either film for the time being, and Aquaman 2 is proceeding as planned regardless of public backlash.
Source: Entertainment Weekly