When does the ‘iddah begin for a woman whose husband went missing then was found dead?

She should start her ‘iddah from the time that he was found
dead, because this is what is certain, and it (‘iddah) is four months and
ten days, during which she also has to observe mourning, unless she is
pregnant, in which case it ends when she gives birth, because Allaah says
(interpretation of the meaning):

“And those of you who die and leave wives behind them,
they (the wives) shall wait (as regards their marriage) for four months and
ten days”

[al-Baqarah 2:234]

“And for those who are pregnant (whether they are divorced
or their husbands are dead), their ‘Iddah (prescribed period) is until they
lay down their burden”

[al-Talaaq 65:4]

And because it is proven that the Prophet (blessings and
peace of Allaah be upon him) advised Subay’ah al-Aslamiyyah that her ‘iddah
had ended when she gave birth. Saheeh, agreed upon. 

And Allaah is the source of strength. End quote.