What is typically done when a voice actor for an ongoing series passes away? 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?)
A similar thing happened with Tomoko Kawakami, who voiced Soi Fong while Bleach was still airing.  While she went on hiatus due to ovarian cancer, she was replaced by Houko Kuwashima.  Once the news of her death broke, Kuwashima assumed the role until the end of the series.

It's a sad day when a seiyuu passes, but the general trend has often been to keep the production going.  Characters are seldom written out of the anime if they are based on an existing media (Bleach, One Piece, etc), so anything that would involve the character not showing up during critical, canonical pieces of content wouldn't be feasible.

The only times I've heard of series being cancelled is when a major player, such as the mangaka, passes away.  This was done in the case of Kaze no Stigma, as Takahiro Yamato had passed away, leaving the series incomplete.