Dead Gods

Divinity is all-but indestructible, and Gods are all-but impossible to kill. All-but impossible is still not impossible, however, and gods can die.
A god, first and foremost, can be slain by another god, who can then steal their power. This is rare, however, for two reasons. One, it sets a precedent, and two, completely destroying and consuming another god is its own challenge. Fragments of 'slain' gods have a habit of coming back, centuries down the line, either as unwanted aspects in their destroyer, or even as independent beings.
Gods can also fade, losing worshippers and losing power, until there is almost nothing left of them. Usually, even this fragment is immortal, but a sudden, catastrophic loss of following - or, as in the case of the halfling creator-god Tzerini, a massive outpouring of power - can induce a sort of shock that effectively kills the god.
Dead gods, those that are not extinguished outright, find themselves consigned to The Abyss, as the World has no more place for them. The Abyss is also deleterious to the health of living gods. It cannot kill them outright, but can trap them and stain their divinity, as happened to Illuvis Once-Divine, a goddess now counted among the Archdevils of the Hells.
Notable dead gods include the Three-Headed Serpent - Stygis, Sythis and Asphyx - a triumvirate of gods who restored their power as patrons of the Ophionic Empire.
The thirteen Dark Lords are more noteworthy still, as the only known gods to have been slain by mortal hands. The Orcs, created as the Dark Lords' soldiers, rose up and slew their gods with weapons known as The Godkillers, which were somehow forged with the destiny of their lineage beaten and folded into the metal in order to wrest that destiny from their creators, breaking their bonds and slaying the gods.