"Forgath's Fortune" is a reference to the fate of Forgath. The fortune is as follows:
"You will die in a great battle with another dwarf. When the serpent becomes your prey, friends will become enemies and love will fuel hate." [1]
It has been reaffirmed by the talking wall in Brassmoon City. [2]
The prophecy is repeated once more by the new teller of the Clan of the Cryptic Fall. Forgath is not present for this telling, but the wording and context are consistent with the first two times the prophecy is told.
This collection of panels discusses the fate of Forgath.