Spoiler for about Rie Tanaka's character:
yea, that was pretty surprising seeing as some of the hype of the series was about that bunch of seiyuu all being involved.
but y'know, the golden rule in TV, especially in a series of this nature: they ain't dead til you see it... and even then they ain't gone forever until the series ends and you never saw them appear again
i'm not saying it'll happen, but i wouldn't be incredibly surprised if Sayara reappeared at some point