Google Vault stores your schools data even if a user deletes and empties their trash.

 

Sign into your google admin account at http://admin.google.com

Click Apps

Now click G Suite

Select and click on Google Vault from the list of Apps

Now click https://ediscovery.google.com/discovery

A new page opens

Click Retention - top left

Set your retention rules for Mail, Drive, Groups and Hangouts Chat by clicking the pencil icon for each rule

Set all retention rules to Indefinitely as screenshot

All set up. You're admin users will always be able to recover deleted files