If a faction is responsible for the defeat of its own units or spires, no reward is gained by anybody unless a talent specifies otherwise.

An example of such a talent is the Narora's Assimilate, which says "When another unit is defeated within 2 hexes of this unit, you gain the Source reward." In this case, even if the unit was defeated by its own faction, the Narora get the Source reward for the defeat (any other reward would still be lost).