Once you have deleted a template, it will no longer be available to your users to generate reports. You cannot undo the action of deleting a template.
If you want to still keep a copy of the template, you can export the template before you delete it.
You can follow these steps to delete a report template.
Navigate to the Templates page.
Click on the Delete link next to the report you want to delete.
A pop-up window will ask you to confirm your choice. If you wish to delete the template, click the OK button. Otherwise click the Cancel link.