This was a oneshot, but I'm not sure if it belonged to a larger collection of similar concepts or not. Might've been part of a challenge posted around here somewhere.

The premise was that both Voldemort and Harry disappeared, but the overall conflict escalated. Somehow Draco Malfoy became allied with the remnants of the Order of the Phoenix, now led by Hermione. She's increasingly cynical and desperate, especially after the recent death of Ron. Her behavior is increasingly reminiscent of others he'd known, so Malfoy suspects she's been delving into Dark Arts. He breaks into her workroom and finds her notes hidden behind a polarized mirror. They reveal that she'd been researching Bloodline Curses, seemingly to destroy all their Pureblood enemies in one stroke- everyone she cares about is already dead, and she's past caring about collateral.

Can't remember if it ended there, or if there was additional setup.