I agree things are looking very dim.
That said I don't see the notification of next of kin says any more than the public announcement by the airline that they lost contact with the plane hours ago and a SAR has been launched. I don't know about standard practice but in this age of social media and quick spread of news, it seems unlikely any airline would want next of kin feeling you don't care. So the contact will begin soon after the announcement, if not before.