As many fans know, Grey's Anatomy Season 9 is going to start off with yet another loss: Mark is leaving. Although we don't know whether he dies or leaves for another reason, we're sure his departure will rock Seattle Grace-Mercy West to the core.

One person we expect will be especially affected is his BFF, Derek (Patrick Dempsey). But what will the effect be? Here are a few theories about how Mark’s departure might change Derek.

It might push him closer to his family. We expect to see Derek lean on Meredith (Ellen Pompeo) after the loss of his friend, and we wouldn't be surprised if he ends up spending a lot of extra time with Zola, too — especially if his hand injury keeps him out of the OR for a while.

Will it keep him in Seattle, or push him away? Perhaps losing Mark will convince Derek to stay in Seattle to bond with the few friends he has left. Plus, if Mark is gone, who will Derek sell the dream house to? On the other hand, Mark leaving might make Derek feel like he really has no reason to stay. We could see it going either way.

A new bromance? One way or the other, we suspect MerDer won't actually leave Seattle in the long run. In that case, we kind of hope to see Derek form a new bromance. Perhaps he and Owen (Kevin McKidd) will continue the friendship they started in Season 8. Or maybe he and Jackson (Jesse Williams) will bond over the loss of their close friend...

What do you want to see from Derek next year? Let us know in the comments below.

Grey’s Anatomy Season 9 will premiere on Thursday, September 27 at 9 p.m. ET/PT on ABC.

Rebecca Martin is an editor at Wetpaint Entertainment. Follow her on Twitter @BeccaMartin47.

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