Aldrich half reached out towards Deimos, perhaps some small shade of him wanting to help someone that had been just like him, but he stopped as combat instinct kicked in. There was no saving Deimos.
In fact, it was likely that Nilah had complete control over Deimos this whole time. She had been letting Deimos struggle just for her amusement.
For that was how demons were. Inhuman in the sense that they were so beyond humanity it was nigh impossible for their horned kind to ever relate to mortal blood and struggle. In the same way that people perceived ants, demons perceived people with an indiscriminate coldness that often manifested as cruelty, though at its heart, it was mostly indifference.
Aldrich could relate to that too.