Sandra Oh, Ellen Pompeo

As Grey's Anatomy winds toward its Season 8 finale, the major question is not only which actors will return next season, but also which residents will actually pass the medical boards in order to become full-fledged doctors — and hopefully, continue walking the halls of Seattle Grace.

"You're going to see how each person deals with [the boards]," creator Shonda Rhimes tells TVGuide.com. "How some of them rise to the occasion, how some of them crack, and some of the problems they're going to be facing."

Anatomy of Shonda Rhimes, the busiest woman in Hollywood

For Meredith (Ellen Pompeo), the boards won't go as smoothly as she hopes when she faces a crisis during her exams. But that's not the only predicament Meredith will face as her "graduation" looms in the very near future. "It's going to be interesting for her," Rhimes says. "Seattle Grace is her home. These people are her family. That's what she spent the past eight years establishing. The idea of leaving or staying is going to weigh heavily on her and going to be pretty hard for her to deal with."

The good news: Meredith's loving husband Derek (Patrick Dempsey) is very supportive of whatever decision she makes, be it staying at Seattle Grace or venturing onward. "Derek would go with her wherever, and Derek is encouraging her to take the best job there is, wherever that is," Pompeo says. On the other hand, leaving Seattle could mean separating the true power couple of Grey's — Meredith and Cristina (Sandra Oh). That very subject will be addressed in an upcoming episode. "There's definitely scenes that reflect ... the relationship between Cristina and Meredith," Pompeo says, noting that no one — aside from the powers that be — knows who will be staying or going.

For her part, Cristina will have the pick of the litter, as multiple hospitals will be wooing her. That will weigh heavily on both her mentor, Teddy (Kim Raver), and her husband, Owen (Kevin McKidd). "It's hard for both of them," Rhimes says. "Cristina is very gifted and a lot of people are going to want her. For both Teddy and Owen, there's going to be some struggle there in terms of letting go. Or if you can let go or if you should let go."

As far as Owen goes, letting go may not be his decision. Cristina and Owen have faced their toughest year yet following her choice to have an abortion and his reveal that he cheated on her. Oh said it may all come down to Cristina deciding between work and love. "Cristina will eventually have to decide what's going to happen in the relationship versus what she wants in her career," she says.

Grey's Anatomy star Sandra Oh: Cristina and Owen head to couples therapy!

While the residents are off taking their boards, the attendings will have problems of their own. "Teddy and Owen still have issues to work out, and we have a lovely Callie-Arizona [Sara Ramirez and Jessica Capshaw] story coming up," Rhimes says. "There's going to be some definite surprises in store for the Chief [James Pickens Jr.] and Catherine Avery [Debbie Allen], Jackson's mom." Plus: Loretta Devine will reprise her role once again as the Chief's Alzheimer's stricken wife Adele. "That's going to be beautiful," Rhimes says.

With the fate of many Seattle Grace doctors up in the air, Rhimes is finding it extra difficult to map out the season finale. "There's a sense of nostalgia there that's really big in terms of these interns no longer being residents anymore," she says. "That alone is a big deal for us. It's also just difficult in terms of what we're trying to do in this finale. What we're trying to do is pretty large and the idea that we're pulling things apart and putting things back together in this very interesting way is not easy."

One thing Rhimes can promise: The hospital will live to see another day. "I'm not going to blow up Seattle Grace," she says.

Grey's Anatomy returns Thursday at 9/8c on ABC, followed by the series premiere of Rhimes' new drama Scandal.