Question: A man remained absent from his wife for a long period of time, and then divorced her without informing her (or anyone else). So does the divorce stand?
Response: The divorce stands even if he did not inform his wife. If a person pronounces the divorce and says: “I have divorced my wife”, then she is divorced whether she knows about it or not. And because of this, should this wife not have known about the divorce except after three menstrual cycles have passed, then she has spent her ‘iddah (waiting period), even if she did not know. Likewise, if a man dies and his wife does not know about his death except after her ‘iddahhas passed, then there is no (further) ‘iddah for her, since her ‘iddah has finished by the passing of the (required three menstrual cycles) time period.
Shaykh Ibn ‘Uthaymeen
Fataawa Muhimmah li-Nisaa. al-Ummah – Page 169 .fatwaonline.com