It was recently reported that Matsuki Miyu, a voice actress, has passed away, perhaps from pneumonia or related complications (RIP). She voice-acted key characters in as-yet-incomplete shows, including at least Prisma Illya (Sapphire).
This surely can't be the first time this has happened. What is typically done when a voice actor for an ongoing series (ongoing either in the sense of a continuously-aired show like One Piece or a show with future scheduled seasons like [currently] Prisma Illya) passes away?
(I see three main options - put in a new voice actor for the character; write the character out of the show; or, worst case, cancel the show altogether. But all three options are imperfect. Historically, what has been done in these situations?)