OneDrive has the capability to hold content of a user account for a desired period of time which was removed from Active directory. As an Office 365 Admin, you can control the retention period in organization level. To do this, you can follow these simple steps.
Open up Office 365 Admin center from the browser and head on to Storage blade.
Expand the navigation with “Show all” option.
Head on to “All admin centers”
Click on “OneDrive” Admin Center
Navigate to Storage tab. You will see the default retention period here. If you wish to extend the period for any deleted user, go ahead and change the value to desired period of time and save it.
Read this post to understand the fundamental things to be considered when deleting a user account from Office 365.
DISCLAIMER NOTE: This is an enthusiast post and is not sponsored by Microsoft or any other vendor.