This is an important option, especially for graduating seniors, or those leaving the district. 

Click the check box under "Files" to select all files. Click "download". See a screen shot here. 

No, teachers should archive all exemplars prior to a student's exit. 

Students can export OneNotes as a PDF document, or as a OneNote file to be imported to a personal OneNote. Export Options

Students will lose access to thier district accounts upon leaving the school district. For graduating seniors, this date is typically mid July to allow students time to save files they would like to keep. A firm date is announced each school year as graduation approaches.