In an interview with The Hollywood Reporter, Glee's over-extended head gay Ryan Murphy says that Finn, Rachel, Babygay Kurt, "and others" will graduate at the end of season three, meaning stars Cory Monteith, Lea Michele, and Chris Colfer are getting the heave-ho.
This would be the first show I can think of about high school in which characters would graduate on time (though about a decade after each actor graduated) and never came back, just like real life. Glee has never been good at realism, but kudos for this. Murphy said "more characters are leaving than are staying," and that we'll know who will get a diploma and who won't in the season premiere. Here's praying that Brittany is held back for years and years to come.
Murphy also said to expect season three to be less about the kid's love lives and more about their plans after high school, and that we'll get to meet some more of their parents as well. Sounds hopeful, but that's the thing about Glee, it always sounds great right before it breaks your heart.