One person we expect will be especially affected is Jackson (Jesse Williams). He's already lost someone he cares about in Lexie (Chyler Leigh); losing his mentor, too, is sure to have a huge impact on him. But what will the effect be?
Here are a few theories about how Mark leaving might change Jackson.
Keeping him in Seattle: We'd already suspected something about the plane crash would keep Jackson around, and now we think that it's going to be Mark's death or departure. With Mark gone, there's a lot of room for Jackson to step up at take a leadership role in the plastics department — and there might be more money for Owen (Kevin McKidd) to woo him with, too.
Jackson steps up: In that same spirit, we'd really love to see Jackson gain some real confidence over the course of the season. He'll never be able to replace Mark, but it would be nice if he starts to fill his shoes, surgically.
A new superior? That said, we're not convinced Jackson is ready to be the primary plastics surgeon at Seattle Grace-Mercy West. It might be interesting to see him have to interact with another older doctor. Mark and Jackson were so close that we suspect there would be a lot of interesting friction between Jackson and anyone who tries to step into Mark's place.
Anger: We wonder if we'll see a darker side to Jackson this season. If Mark leaves voluntarily, we could see Jackson being bitter about that; if Mark dies, we could see him carrying around a bit of a chip on his shoulder about the unfairness of the world, at least for a little while.
Will it drive him to April? Shonda Rhimes has hinted that the writers are going to explore the Jackson/April (Sarah Drew) relationship further. Perhaps it is the loss of Mark that drives Jackson back into April's arms for comfort.
What do you want to see from Jackson next year? Let us know in the comments below.