So I've had this idea in my mind for quite a while. Harry, in attempting to save ginny, either gets ambushed by tom and the basilisk with some kind of ritual to increase the petrification abilities (possibly preempted by tom finding out harry is a horcrux) or just catching the indirect gaze of the serpent while fighting it. Either way, he gets petrified and left in the chamber for ages before it finally wears off, leaving him stranded in the distant future.

Could just be a distant future version of the hpverse, or a segue into a crossover, but it seems like an interesting idea to me.

Without Harry to stop him, Voldemort conquers Britain, then the world. Unstoppable and immortal, countless centuries pass under Voldemort's cruel reign.

All wizards are pure-bloods now, only a tiny number of untrained muggleborns exist in the doomed to fail resistance movement.

The muggles themselves are nothing more than slaves or even livestock. Their grand armies and powerful weapons are now relics of an ancient past.

Eventually, the venerable and ancient basilisk, one of the symbols of Voldemort's regime, succumbs to old age and dies and somewhere, buried under an ancient ruin in a land where nothing grows, a twelve-year-old boy awakens. Can he fulfill his destiny when it seems there is no hope? Isn't he hundreds of years too late to defeat the ruler of the world? Can he find any allies in the subjugated people living under the boot of living gods?

Harry let the house elf lead him through the dark hallways. At least, he thought it was a house elf, it did bear a resemblance to Dobby, but he would never have imagined Dobby to wear a sword on his belt.

"I've brought the boy, mistress," the elf said, opening the door at the end of the corridor and beckoning Harry through. Stepping into the dark room, Harry waited for his eyes to adjust.

"They say you saved a family of muggles from a wizard."

Harry strained his eyes, trying to spot the owner of the voice. Whoever it was sounded old.

"Too bad they'll kill ten more families in retribution for your defying them," the voice said again."

Then he spotted her, busying herself in the far corner of the room, facing away from him

"I don't like bullies," Harry said defiantly.

"Merlin, you're young," the other person said. Harry suddenly realised that he wasn't struggling to understand the words she used. "Now, come here and let me get a look at you."

Harry stepped forward and suddenly a bright light filled the whole room. Harry blinked to clear his eyes at the sudden assault on his eyes.

The old woman, and it was a woman, Harry thought, stepped closer to him. Harry was wrong, she wasn't old, she was ancient. He didn't think that people could get so old.

The woman peered at him, her eyes hidden behind hundreds of wrinkles.

There was a moment their eyes met and then, suddenly, her eyes widened in a show of some emotion and she started coughing terribly. She turned away from Harry, blinding reaching for something. Harry took a step forward, unsure of if, or how, he should help. After a moment, she found a vial of something on a table in a corner and drank it like a person dying of thirst.

"Are you okay? Can I do anything to help?" Harry asked uncertainly.

"I'm fine. I'm fine. It'd take more than a coughing fit to kill me, Harry."

"You know who I am?" Harry asked in confusion.

"Of course I do," the woman said, straightening up and approaching him, the ghost of a smile on her face. "You saved me from a troll once."

"Hermione?!"