It's important to understand what happens behind the scenes when a user is deleted from Azure AD. Failure to properly control this process can result in the permanent loss of a user's mailbox or other important data.
First, when a user is deleted, the account does not disappear. It is moved to the user recycle bin. These users can be restored to active status at any time.
If no other action is taken, deleted accounts will remain in the recycle bin for up to 30 days. However, it is possible for you to permanently delete them. It is also possible that the account may be permanently deleted if a new account with the same username is created. (Those using AD Connect should pay special attention to this second possibility, ...
