One of our corpses is missing

An alarm bell trips at the entrance of the secret passageway and, despite the distance, the Drow priestess silently signals for the surviving ten Death-cultists to head back up the main tunnel.
Their mission; to confirm the adventurers claims. To see for themselves that the Dragon’s skull is indeed destroyed.
Cautiously, they creep uphill through the darkness and re-enter the cave, half expecting a trap.
After their recent, disastrous encounter, they’re relieved that the would-be-heroes are gone.
Let the Drow deal with them.

They quickly find and examine the fractured remnants of the skull.

“Damn it! Our plans are ruined!” hisses one of them.

“No matter” responds his compatriot. “We always have plan B to fall back on and frankly, I much prefer it anyway. Proper drama. A helpless woman being bound and sacrificed on a blood-stained altar. It’s classic!” 

As they’re chatting, they go to work searching through the dead bodies piled up around the outer edges of the cavern.

“Found her!” one of them shouts.

Rolling out a stretcher, several of the Nerull worshippers, lay the lifeless husk of the Dragon disciple across it, her head hanging at an unnatural, broken necked angle. Four of them lift her up and slowly begin the hike back to the staging area.

“Don’t worry Teala, Lady Death’ll be more than happy to send you back.”, the lead cultist whispers in her unhearing ear.

“What about the priests, our Fly riders: Crawley & Kotow?” asks one of the other searchers.

“Sod them.", replies another. “They were just middle-management.”