From: Rabbi Moshe Sofer
To: Pressburg
R' Leib Hersh of Kitzeh fell from a boat into a river and disappeared; a body was later found with matching garments and documents. The Chasam Sofer rules that the combined weight of eyewitness testimony of the drowning, the search conducted, prolonged observation, matching garment pieces, identifying initials, and personal documents removes the Biblical prohibition of eishes ish, leaving only a Rabbinic stringency, which the simanim are sufficient to override. The woman is permitted to remarry after waiting twelve months from the date of the drowning.
Source: Shu"t Chasam Sofer EH I §65