Vault is not a service for normal user, it helps administrators to retain data as long as they need even though the data owner already deleted them. Currently, the data retention policies of all university members for Google services are "forever" which mean all of your data, including Gmail, Drive, Chats will never been purged. When users delete their data, they will be just hidden from their owner and also recover the owner's storage space (which is unlimited for the education members), but the data will not be "exactly" deleted from the system. The administrators still able to find them if required, i.e, by law. In additional, the user who accidentally delete their data can request for data recovery as well. However, we cannot guarantee that the data can be 100% restored.
Please be noted that, this is a Google feature which cannot be controlled by the university so it can be changed or discontinued anytime.