The Devils

Seem to be unaware of Bethany's importance, treat her as secondary to Riga. Until they refer to her a "both spoils at once".

A number of devils exiled / trapped onto the material, possibly for centuries.

Have been tracking Riga at least since Troval, possibly earlier.

They think Riga is the only mortal they need for their return to the Nine Hells:
Why? Ritual? Bargain?

Probably exiled for centuries, likely even earlier than the Draconic Wars.

The dead Fiends did not burn up / melt / vanish, and even removing the Planar Binding Fiend Core only caused a partial effect. Ordo thinks they are puppets, Riga theorizes it might be due to prolonged exposure/exile to the Material. Azzrukhan mentioned that the Fiendish Gargoyles were "reduced" too, weighed by stone.