From: Rabbi Moshe Sofer
To: Rabbi Yosef Yoel
A woman whose apostate husband disappeared and was reported dead by his observant son sought to remarry without chalitzah from the mumar yavam's brother. The Chasam Sofer rules unequivocally that a single witness testifying to the death of a mumar yavam is sufficient to permit the yevamah to remarry, relying on the Maharik, Beis Yosef, and Shulchan Aruch EH 158, and invoking two combined majorities (terei ruba) to prevent her from remaining an agunah.
Source: Shu"t Chasam Sofer EH II §74