You may already know that you can have notification when a files mass deletion occurs (thanks to the Security & Compliance alert).
Well, this is going to get better as this alert is being sent only after the mass deletion has been executed and is being sent to administrators.
OneDrive for Business client is going to get an update to notify end-users when a files mass deletion (more than 200 files) occurs.
This update will be rolled out starting February 2019.
When mass deletion is detected by the OneDrive client, end-user will be prompted to confirm it.
If this was intentional, the user will have to confirm the deletion by hitting the Remove button; if it was accidental, the deletion can be cancelled and files being restored by hitting the Restore files button.
End-user will also have the ability to always delete files, even if a mass deletion is detected, by checking the Always remove files option. I hope this will be manageable by some GPO settings as this is quite dangerous option.