From: Rabbi Moshe Sofer
To: Rabbi Tuviah Katz
A husband whose wife disappeared after two years of marriage, leaving no trace after five years of searching, sought permission to remarry without the costly heter meah rabbonim. The Chasam Sofer ruled leniently, permitting remarriage based on a combination of factors including multiple doubts regarding the cherem of Rabbeinu Gershom, the wife's alleged physical incapacity, and the husband's unfulfilled mitzvah of piryah v'rivyah, subject to conditions including depositing the kesubah, issuing a zikui get, and taking an oath regarding the wife's possible insanity.
Source: Shu"t Chasam Sofer EH II §99