Very unpopular opinion, but a hill I will die on.
The quality of Community dropped considerably when Pierce wasn't a part of the main cast. His criticisms of the writing were often on the money, as the payoff he'd often get from being the father figure to Jeff (e.g. the barber episode) or the unsuspecting hero (Paintball) were some of the best. When he was allowed to be human he was great, when he was a pure asshole it was lazy.
Yes, Chevy Chase is a monumental cunt...but that was close to a decade ago now. The "young" Annie is played by a woman in her forties with a 20+ year career in acting, and the entire cast is essentially a who's who of Hollywood and TV elite right now. Everyone has moved on, and Chase did an interview years ago stating that he'd learned from his isolation and wanted one more shot at work. He did some stuff for Netflix that went well, so he's not completely out of Hollywood. Let's not forget that Harmon was fired because he was a cunt too - a cunt that showed up Chase in front of his family, alongside abusing a writer that didn't want to have sex with him while he was a man in a committed relationship. He gets a pass because of his writing abilities, so why shouldn't Chase get another chance?
IMO Harmon should reach out and ask Chase to be in the movie. Have him sign a deal to say that he'll get nothing if he's abusive or racist on set, and let him end his career on a high. Having Pierce alive would almost certainly be a plot for a movie in itself.