Anna Faris surprised everyone by announcing during the long period between Seasons 7 and 8 that she would not return to her leading role as Christy Plunkett in Season 8. The show wrote Christy out of the story by having the character accept a full scholarship to Georgetown Law School and move to Washington, DC; Faris did not return to the show in what turned out to be its 8th and final season.
Anna Faris originally said that she left the show between the 7th and 8th seasons to pursue new opportunities. She later confirmed that the real reason was that she was going through a lot of turmoil and needed a break from acting altogether.
The show had originally planned on a recurring Season 8 storyline involving Tammy Diffendorf's father, an alcoholic who killed her mom and was imprisoned leading Tammy to be forced into the foster care system. The plan was aborted when the producers couldn't find an actor whom they liked for the part. In the end, the story began and ended with just 1 scene in the S8 premiere when Tammy accepts a phone call from her father wishing her a happy birthday and they talk briefly. His voice was not heard here.
The producers originally planned for Season 8 to include a multi-episode arc that would feature the father of Kristen Johnston's Tammy character, who was to be released from prison after spending over 20 years behind bars for killing Tammy's mom. But the casting process didn't turn up an actor who anyone liked for the role. In the end, the story was capped at a single phone call between them (her father called from prison to wish Tammy a happy birthday, and she took the call after considering not doing so) in the S8 premiere.