When a player character dies (ally or otherwise) you can use their corpse for Werewolf's Devour synergy, Templar's Repentance ability, or any of the Necromancer corpse consuming abilities, but Companions do not let you use any sort of corpse consuming ability on them.
Here's what it looks like to have your Companion fall in combat:
And here's what freshly-slain corpses
usually look like:
For reference, an eligible corpse glows red while in Werewolf form, glows yellow if Repentance is slotted in the human form, or glows blue when any Necromancer corpse consuming ability is slotted in the human form while Repentance is not slotted:
Since I'm in Werewolf form, the corpse glows red if it's eligible to be consumed, and I get the option to use the Devour synergy if my crosshair is over the corpse. However, Companions never let you use corpse abilities on them, even when fallen players and NPCs do. In the case of allied players, you get the option of using corpse abilities on them or resurrecting them, so it's bizarre that Companions
only give you the option of resurrecting them without letting you use corpse abilities on them.
I want to be able to use corpse abilities on fallen Companions because it would be useful in combat, and it's already possible to use corpse abilities on fallen allied players. Plus, it would be fun to use corpse abilities like Devour or Bitter Harvest on the Companions we don't like.