|The following is based on Fallout Tactics and some details might contradict canon.|
Sometime after their departure, Gammorin's mutants were pursued by Brotherhood of Steel airships. While most of them ended up in the vicinity of Chicago, far from Gammorin's forces, one of the zeppelins crashed north of the mutant encampment. The leader, Paladin Latham, challenged Gammorin to a single unarmed combat and, to surprise of everyone, killed the mighty mutant.
Gammorin is mentioned only in Fallout Tactics: Brotherhood of Steel.