In this year of chaos, abrupt TV cast changes aren't the most wild thing we're dealing with. But Anna Faris's abrupt announcement that she would not be returning to the CBS sitcom in which she's been starring since 2013 did throw a lot of people for a loop last summer — especially considering that she's, y'know, the titular Mom. But the series, as seen in the Season 8 premiere, has handled the pivot with a degree of grace, entirely because technically, Faris's character wasn't the only mother on the show, and her co-…