"Cory Monteith, Lea Michele and Chris Colfer are all seniors. Despite what co-creator Ryan Murphy told The Hollywood Reporter about the fate of the trio during a prior interview, co-creator and executive producer Brad Falchuk said [during a panel at Comic-Con in San Diego on Sunday, July 24, 2011]: ‘They are not done with the show after this season.’ "
The article continues, " ‘Because they’re graduating doesn’t mean they’re leaving the show. If you have Lea Michele under contract, you don’t just say, ‘We’re going to let you go.’ ‘ Falchuk noted that there are a number of ‘Glee’ kids, with some seniors and some juniors – like Jenna Ushkowitz – and a ‘number of original people are not graduating. It was never our plan, it was never our intention to let them go,’ Falchuk said. ‘They are not done with the show after this [upcoming]season.’ "
This fall will be season three for "Glee." Then, season four would air during the 2012-2013 season.
As you can read in Goldberg’s earlier interview with Murphy, he certainly made it sound as if the three stars would be leaving after season three. In that interview Murphy is quoted as telling Goldberg the following:
THR: Will we see a Season 4 with Chris Colfer (Kurt) and Lea Michele (Rachel)?
THR: We will not?
Murphy: They are graduating.
THR: What about Cory Monteith?
Murphy: Cory is graduating. Those are the only three I’m going to say.
THR: They’re not going to be back at all in Season 4?