If you lost or deleted a user account from Office 365, recover the user's OneDrive, Calendar, Outlook, and Tasks data using the import function. Make sure to select a snapshot from a time before the user account was lost or deleted.
Re-create the user in Microsoft and then import data back to the user from an appropriate snapshot.
Note: It is not possible to use the restore function (restore in place) because when you re-create the user in Microsoft, it receives a new user ID. Keepit can only restore user data in place if the IDs are the same (i.e., if the original user still exists).
For a step-by-step guide on how to import data, see: How to import Office 365 data