From: Rabbi Moshe Sofer
To: Rabbi Wolf
A group that leased the right to collect a sheep-slaughter excise tax suffered losses when a livestock plague and the lord's dumping of sheep undercut the entire trade. The Chasam Sofer rules this is a classic makas medinah, entitling the lessees to withdraw from the lease going forward and pay only proportionally for the period the lease was operative; however, silence after the calamity constitutes acceptance for that period, and the muchzak principle does not apply here since the lessees had no ability to generate any revenue whatsoever.
Source: Shu"t Chasam Sofer CM §161