Summary:
Harry wastes no time taking the steps needed to safeguard a better world.
Harry's wand was out as he materialized, as was the word Expelliarmus. Just like that, he had the powerful, but evil wand caught in his left hand. Before Snape could react, he was stunned. Seven times. Harry alternated throwing powerful spells at Dumbledore to keep him from having enough time to draw a back-up wand.
Kill them with fire. Kill them with fire. It kept running through his mind. But Fiendfyre would be overkill within Hogwarts. He spoke nonsense in Parseltongue as he waved his wand in an intricate but meaningless pattern. At the same time, with two fingers of his left hand he stuffed a torn-off sleeve into the Headmaster's bottle of Firewhiskey and set it on fire with the Elder Wand and a muttered Incendio. He knew being covered in fire would only slow the old man down for a short reprieve.
I know where I want to get rid of him, but how would I get him to a remote island? He looked over at Snape. Gellert Grindlewald, Severus Snape. Two people that can do no wrong in his world. Dumbledore likes Bad Boys! he realised. He'd probably be able to follow their trail as he disapparated with the unconscious Potions master.
And so it worked out. Dumbledore could not locate where Snape was stowed without searching on foot. A Point-Me spell would only tell him the rough location on the magically shrouded desert island.
Meanwhile, Harry was piggy-backing on the largest satellite he could find. He'd purloined a medium-sized nuclear missile. He had once been shown - by Hermione - the nested differential equations and frames of reference for even the simplest rocketry, but thanks to Magic, he could visualize the island, point it in the rough direction it would have to travel, and it would land and detonate where Dumbledore was hunting down his pet Death Eater.
Harry had calculated his orbit very roughly, but he did come over the horizon in time to view the fireball (with conjured dark glasses). It should have been a horrifying sight.
It's more like the beacon of Liberty, Harry thought. He saluted Dumbledore smartly. Voldemort had been a doddle compared to the Chief Warlock and unelected dictator of Britain's medieval kingdom of magical horrors. He guessed that this time around he'd have Tom Riddle gone forever by dinner time.
He had fantasized about destroying Dumbledore's reputation, but finally decided that forgetting him was far safer. He had liquidated the publisher of the Harry Potter Adventures series and kept their presses and distribution agreements. It should take only a few years to remove Dumbledore from all the Wizarding histories. I didn't make the system, I just have to live with it.
He comforted Hermione when she came to him with the news that the Headmaster was missing. Soberly, he told her that meant they had to settle affairs with Voldemort by themselves. Ron was nowhere in sight, so he told her time was of the essence and popped off to Black Island with her before she could object.
Life was idyllic as they researched the facts Harry'd learned decades ago, by his subjective time. Eventually, Hermione asked him about the Island on the horizon that appeared to be covered with glass.
"An evil wizard died there with his closest servant," he explained. "This is a great place to live, but it's also an outpost. Dark lords sometimes don't stay dead."
Note: It was the only way to be sure.