The link stops working immediately, and anyone who tries to open it sees that the report was not found. Deletion is permanent: there is no trash and no way to restore it later, although your campaign data stays intact in Meta and Google. To delete, click the trash icon on the report card and confirm.

If you only want to cut off the client's access for a while (late payment, paused contract), don't delete the report. Use the Active / Deactivated switch on the card instead. When it's deactivated, the link won't open, even with the password, and you can reactivate the same link whenever you want.