Former SFUSD employees are not granted access to district systems after their employment with the SFUSD had ended. This applies all systems that an employee may have had access to during their employment including their SFUSD Gmail account, and content stored in their Google Drive (Docs, Sheets, Slides, Forms, Classroom, etc.)
If email or other documents need to be retained by a departing employee, the employee must make backup or personal copies prior to the end of their employment. The following link provides details for making backup copies of Gmail and other content stored in Google Documents, Sheets, etc.: Google Takeout.