Grey's Anatomy and Private Practice creator Shonda Rhimes is a busy woman.

Her new ABC series, Scandal, debuts April 5, and she's got several pilots in the works. As for her flagship show, most of the Grey's Anatomy cast is taking part in the March 18 musical charity event held at UCLA.

The title, in homage to 2011's "The Song Beneath the Song", is Grey's Anatomy: The Songs Beneath the Show. It will benefit The Actors Fund and nearly the entire cast is lined up to participate in the special concert.

Even more exciting, she's confident all the cast wants to return for Season 9.

Excerpts from Rhimes' interview with TV Guide below ...

On how the charity event came about: "When we did the musical episode last season, we discovered we had way more singing talent than we ever imagined ... the entire cast, with the exceptions of Patrick Dempsey, Ellen Pompeo and Jesse Williams, who has a prior commitment, is on board and pretty excited."

It's unclear why Ellen and Patrick will be absent, but "Sara Ramirez, Kevin McKidd, Justin Chambers, Chyler Leigh and Jessica Capshaw are all going to sing. Sandra Oh has stated she's not a singer, so she'll do a couple special things."

"Eric Dane, Sarah Drew, James Pickens Jr., Kim Raver and Chandra Wilson will also take the stage."

On whether Patrick and Ellen will be back next season: "I have no idea. I have my fingers crossed. What I think is really lovely is that everybody wants to come back. There's [money] stuff happening."

"I am [confident], but I have a plan in place for the finale that can occur regardless of who is staying. Our goal is to have Derek and Meredith move in to the completed dream house. [A real L.A. home will be used.] And our residents will be interviewing for jobs all around the country."

On whether Katherine Heigl's desire to return will be realized: "I think it was really nice to hear her appreciating the show. At the same time we are on a track we have been planning."

"The idea of changing that track is not something we are interested in right now."

On whether Addison will have a baby on Private Practice: "I will say this: That journey is going to be completed by the time the season is over, and I think fans will be very satisfied.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.