I don't think I have ever heard of the last episode of an animated TV series being shown in a movie theater. I think it is difficult to make a big deal out of it, especially once it has been aired on TV. However, I can't say that it is completely impossible, since recent anime sometimes have special screenings for a short period of time. For example, Delicious in Dungeon will be shown in movie theaters in December, and although it is not AoT, I think it is possible for Demon Slayer to be shown in movie theaters for the final time.