 O 'Malley dies in the premiere of the sixth season , due to injuries sustained by being hit by a bus , and Stevens later departs Seattle after being diagnosed with cancer and following a lack of communication between her then husband Karev following the Seattle Grace merger with Mercy West . Several new characters are introduced as Seattle Grace Hospital merges with Mercy West . Residents April Kepner and Jackson Avery both transfer to Seattle Grace Hospital from Mercy West , and the latter entertains a brief relationship with Lexie Grey , until she reunites with Mark Sloan . Subsequently , Teddy Altman is introduced as the new Chief of Cardiothoracic Surgery . In the season six finale , a deceased patient 's grieving husband embarks on a shooting spree at the hospital , injuring Karev , Shepherd , and Hunt , and killing residents Charles Percy and Reed Adamson . In the shooting 's emotional reverberations , Hunt and Yang abruptly marry , not wanting to risk separation . Torres and Robbins eventually wed , officiated by Bailey . In season eight , Webber steps down and allocates his job to Hunt . As the final year of residency for Meredith , Yang , Karev , Avery , and Kepner is coming to a close , the doctors are all planning to relocate to different hospitals to pursue their specialty careers . However , all plans are put on hold when several doctors from Seattle Grace Mercy West Hospital are engaged in a plane crash , which kills Lexie and endangers Meredith , Shepherd , Yang , Robbins , and Sloan . At the conclusion of the eighth season , Altman is courteously fired by Hunt as she struggles to decide whether or not to take the job as Chief at the United States Army Medical Command ( MEDCOM ) . In the season nine premiere , Sloan dies due to sustained injuries from the plane crash following a brief relapse of temporary health ( the surge ) and the remaining characters work through their post traumatic stress and Arizona Robbins ' loss of limb by way of suing Seattle Grace Mercy West as the hospital was responsible for putting the surgeons on the plane . The season continues with the struggle of the lawsuit and the animosity that it creates within the hospital , Yang and Hunt eventually divorce in order to help the lawsuit . Robbins cheats on Torres with a visiting facial reconstruction specialist . The doctors who were on the plane won the lawsuit , but the pay out bankrupts the hospital . They all club together and buy Seattle Grace Mercy West , with the help of the Harper Avery Foundation , and they become the Board of Directors , once being called the " Grey @-@ Sloan 7 " . One of the changes they implement is renaming the hospital to Grey Sloan Memorial Hospital . Grey 's Anatomy then concluded its 10th season on ABC and saw the departure of one of its major players , Cristina Yang , played by Sandra Oh . Towards the end of the eleventh season , Derek Shepherd witnesses a car accident and pulls over to help the injured , but his car is hit by a truck with him inside as he attempts to leave the scene . He later dies at another hospital following the doctors ' mishandling of his injuries . The season 12 finale saw the departure of one of the show 's longest running characters , Callie Torres , played by Sara Ramirez . 
