According to TV Line, Grey's Anatomy will be switching things up in an upcoming episode where all the characters will be caught up in an alternate reality:
In a February 2012 sweeps episode, the docs at Seattle Grace will be making their rounds in an alternate reality, as the ABC drama ponders the provocative question, “What if things had been different — very different.”
[...] Other Grey’s alums will be back — including a certain victim of the Seattle Grace Massacre of 2010, who shall not be named. (Follow me [Michael Ausiello] on Twitter for clues.)
In the episode we will get to see what Meredith's life would have been like if her mother never had Alzheimer's and if Derek and Addison had stayed married.
No word yet on what Cristina Yangs's What-if scenario will be. What are your guesses, dear peeps? What scenario would you like to see?
