The treatment of other gods as demons was an entirely etymological development brought about by the differentiation of the Zoroastrian asuras and the daevas. Its basically about winners and losers - the conquered gods became tainted with evil, while the victorious gods were *obviously* those worthy of worship.

Its interesting that the resurrection of a god is used repeatedly throughout ancient history as a means of reinstating a slain god - Osiris, Marduk (again) and of course Yahweh, who managed it twice.