Author's Note - A lot of people use the idea that the Horcruxes are either, firstly, a equal portion of Voldemort's soul, or a steadily decreasing fraction. However, this is a scary story that uses two parts of the Prophecy...
"He Will Mark Him As His Equal..." and "One Can't Live While The Other Survives..."
Harry had felt uneasy as he'd come closer to this showdown. His magic was not working as it should, but he had to do this. Voldemort stared him down, looking healthier than he had in the graveyard.
"Your horcruxes are destroyed..." Harry stated, Voldemort not even rising to the threat it entailed.
"Oh, I think not..." Voldemort chuckled, "Avada..."
Harry had the curse on his lips at the same time, not even noticing Voldemort state "Cadabra..." instead of "Kedavra..."
As his spell struck, a lancing pain cut through his head, and he collapsed, his body going into convulsions. No-one noticed, of all people, the Death Eaters spirit away the convulsing form of the Boy Who Lived as Voldemort's corpse seemed to collapse.
Ginny wondered what was going on when she heard a knocking at the door of her temporary home a few days later. She smiled as she saw who was there, bowing lightly.
"Shall we?" The figure asked.
A few hours later, the surgery of the Wilkins family was found burnt out while Hermione Granger was found having had an accident where she'd fallen onto some ornamental fencing and been impaled. In the former case, the Dark Mark floated over the building. No-one was sure how they'd located the Granger parents, but it was strongly suspected Hermione's death was anything but an accident.
Meanwhile, Dumbledore found himself in Grimmauld Place, seemingly summoned by Harry Potter. Instead of who he expected, however, the face of Tom Riddle stared out at her, smirking. "Good work, Dumbledore..." He sneered, "You didn't think..."
"What do you mean... Tom?!" Dumbledore's shade asked. "Did you really think the prophecy meant you'd WIN?! My entire soul entered my last remaining horcrux when Harry destroyed that homunculus..."
"Oh my god..." Dumbledore stated, "You..."
"Possessed him, evicted him from his body, and finished claiming Ms. Weasley... Well, Her mother killed Bellatrix..." Riddle stated, "He Will Mark Him As His Equal... We were equal parts of, well, me, when Harry faced me... One Can't Live..."
"While the other survives... When the other soul piece was destroyed..." Dumbledore began, and began sobbing even as he was sent back to the great beyond. The new Lord Voldemort only ever had one Horcrux from then on, which was used in the ritual to resurrect him. And the wizarding world never escaped his tyranny...