Mr. Clark tells Hunt that he'd shoot him first and then Cristina but he really only wanted to kill Derek. He believes this is retribution for his wife's death, which he believes is on Derek's hands. Meredith then comes into the room and tells Mr. Clark to shoot her. She explains that she is Lexie's sister, she is the closest thing Webber has to a daughter, and she is Derek's wife. He turns the gun toward Meredith, but Cristina says Meredith is pregnant. Hunt makes a move toward Mr. Clark and is shot, knocking him unconscious. Cristina and Avery then raise their hands and Avery tells Mr. Clark that Derek will die and he can watch it happen on the monitor. Derek flatlines and Meredith cries almost hysterically. Mr. Clark walks out.

Is it true that does derek die in grey's anatomy season 6?
yes