Laura Vandervoort (Kara) will not be returning as a series regular in Season 8. This confirms speculation that surfaced when she was not on the cast list in the CW's press release.
When we last saw Kara, in "Arctic," she was somewhere within the Phantom Zone.
"They announced the cast... and I'm not a part of it," Vandervoort told TV Guide's Matt Mitovich. "We were all surprised when they chose not to bring me back as a regular, but I'm sure I'll be back for one or two [episodes]!"
Vandervoort seems to have a good attitude about the whole thing. "The show is about Clark Kent, and I was honored to be a part of it. I mean, my character became more than it was supposed to be. She ended up sticking around the entire season," she told Ausiello.