According to
Krytonsite
Michael Rosenbaum (Lex Luthor), Annette O'Toole (Martha Kent), Allison Mack (Chloe), and John Schneider (Jonathan Kent) will all return for the 2 Hour Finale and that Kristin Kreuk (Lana Lang) will not. John Schneider will also be on "Kent" which'll be the first episode when new episodes return on April 15.