To remove a sync or cloud only user from Office 365:
Remove Cloud only User
remove-msoluser –userprincipalname user@dagfriden.se
If the user is syned from OnPrem Active Directory remove the user from the sync scope or delete the user from the Active Directory.
Remove One User From The Recycle Bin:
Get-MsolUser -All -ReturnDeletedUsers | select-object UserPrincipalName,ObjectID
remove-msoluser –ObjectID OID -RemoveFromRecyclebin
Remove All the Users From the Cloud:
get-msoluser | remove-msoluser -force
Remove All the Users From the Recycle Bin:
get-msoluser –returndeletedusers -maxresults unlimited | remove-msoluser -removefromrecyclebin -force
More info can be found at:
https://technet.microsoft.com/en-us/library/mt628068.aspx