According to EW.com's Michael Ausiello, Dustin Milligan's (The Ghostfacers' 'Alan J. Corbett') contract option is not being picked up for 90210's next season. However, it looks like "the door is being left open for the actor to briefly appear in the fall to wrap up Ethan's story."
Milligan, a 90210 regular cast member, plays 'Ethan Ward'.
Source: EW.com.