Although Katherine Heigl was scheduled to return to the 'Grey's Anatomy' set March 1 after three months of maternity leave, "she was not there," a source tells PEOPLE.

Sources told EW's Michael Ausiello that 'Anatomy' creator Shonda Rhimes has agreed to release Heigl from her contract. ABC Studios and Heigl's reps will then hash out a final exit agreement.