There are multiple scenarios where a Theme Builder template might get deleted by mistake or disappear due to a human error.
Deleted or missing Theme Builder templates can be restored with the help of a specialized WordPress plugin, Divi Restore Theme Builder Templates
Download the Divi Restore Theme Builder Templates plugin
Open the Divi Restore Theme Builder Templates plugin's link in your favorite browser
Click on the Code button
Choose the Download ZIP button
Save the plugin's zip on your computer
Note: Safari users should disable the Open save files after downloading option in the General settings of the browser.
Install the Divi Restore Theme Builder Templates plugin
Go to WordPress Dashboard → Plugins → Add New
Click on the Upload Plugin button
Click the Choose File button and find the location of the downloaded ZIP file
Click on the Install Now button
Click on the Activate Plugin button
Restore the Theme Builder Templates
After plugin activation, we will see three new links in the WordPress dashboard menu:
Header Templates
Body Templates
Footer Templates
Each of those links leads to a listing page where you can see what layouts can be restored:
Edit and Save the chosen template to Divi Library
Click the name of the template in the header/body/footer Templates list
Click the Save To Library icon in the Page toolbar
Set a descriptive Name for the layout to be saved in Divi → Divi Library
Click on the Save To Library button
Import the saved (restored) layout from Divi Library to Theme Builder
Go to Divi → Theme Builder
Click Add Global Header/Body/Footer
Choose and click Add From Library
From the Divi Library window, click the Saved Layouts tab and then click the name of the layout you restored
Click Use This Layout button
After the import is completed, click the Save Changes button
Note: Deactivate and delete the plugin from your website once the layout is restored.