Just got out of a game where this happened.
It's mid game, there's 4 cult, 2 town, and the godfather currently alive (7 total).
Teal reveals as marshall. Cult promptly lynches him, then works their way down and lynches the other town and the GF. Instant cult win that day. Much lulz were had.
So we joked that maybe there should be an achievement for this (obviously would be alot harder if cult doesn't have majority).
Something along the lines of, marshall reveals and the mass lynching results in the cult winning that day.
Maybe: Smite the Unbelievers, or Blessed Intervention.