So about this thing.

The reason I've given up writing it is because I found the way it was going to be inherently unsatisfying, dipping below my already rock bottom standards for what a story should be. The reason I found for this is because of how the second part of the story I imagined just would not connect to the first half without ruining the integrity of the main character's motivations. To go into more detail, the 'first half' of the story would be all the scenes involving the plot from the books and the hunt for the horcruxes, while the second half would be starting from the introduction of the vampires and covering a larger planned series of misadventures. The problem here was that ultimately, there was no compelling reason for the Harry here to go on these misadventures. The character as I had set up in the first part of the story would never do such things. He would either have actually run away, or killed himself in response to the ever growing level of anxiety in his life. Both of these endings would have been satisfactory to the character, but wouldn't have given any resolution to the actual plot. Not that the plot was terribly interesting, but still.

(This conflict was something I was aware of when I started writing the story, but I didn't bother resolving it because I mainly wanted to write this thing based on what would be in the first half of the story to begin with.)

Just so I don't forget it, I'll put down how the original second half of the story was supposed to go. So if you really did want to see how the plot would play out or just disagree with me on how the character should have been written, or you want to write your own, better version of the story (you absolute madman), you can have some kind of closure:

Following his encounter with Mira, Harry would have gone to the headquarters of the local vampire middle management at an office building somewhere in London. There he would have met LaCroix, who would have threatened, bribed, or mind controlled him into going to a crypt in northern Africa to look for a magical sword in exchange for their help in the war. In the process of looking through this crypt, Harry would have been tracked by probably Draco Malfoy who would have gotten killed by the guardians of the crypt who would be giant ripoffs of the hammer haunts from Thief as part of a thinly veiled attempt to ramble on about one of my favorite games. Harry would retrieve the sword, which would have the power to instantly kill vampires during the night, and return it to LaCroix. Along the way someone would inform Harry that LaCroix had been planning to intervene in the war all along and that he was just trying to mine free favors out of Harry.

After this, Harry would look for more help for the war as the vampires are afraid of intervening against the giants Voldemort had recruited. A contact of some kind (possibly Nagini who had gained a mind of her own and was looking to have Voldemort overthrown so she could attempt running the world from the shadows) would point him in the direction of the Society of Gilmour, a mixed group of wizards and muggle scientists/engineers who believe that progress would be best made by combining magic with technology, who had been classified as a terrorist group for trying to reveal magic publicly to the world. They would inform Harry that they would be willing to help in the war in exchange for protection from the Ministry after the war so they could work on their experiments freely. They also would need Harry to rescue some of their imprisoned members. This would lead to a prison break from a severely understaffed and Dementor-free Azkaban, ad looking through an abandoned magical mental asylum for plans of a magically enhanced railgun.

With the help of both groups assured, Harry returns to Hogwarts which is now the last bastion of Dumbledore and the old Ministry's regime. To the resignation of some Order members, Dumbledore would accept the help. The Battle of Hogwarts would be fought, but it would instead end up as a massively successful romp for Dumbledore's side, with the Death Eater forces being caught completely off guard. With victory potentially in sight, Dumbledore reveals to Harry his status as the last horcrux. After drinking a bunch, Harry resolves to try torturing Voldemort into insanity himself instead of facing his own death. He locates Voldemort using his scar in some kind of hideout and attempts to storm the place using a magically enhanced MP5 and a lot of fire, but ends up caught by Voldemort. Voldemort tries to kill him, but instead takes out the horcrux. Either the shock of failing to kill Harry a second time of being interrupted by Nagini results in him fleeing (to be hunted down by vampires later) or being captured and fed to Dementors.

After this, a surviving Harry watches as the vampires start rebuilding the wizarding world in such a manner so that the events of the books could never happen again, by severely stripping down the Hogwarts curriculum, planting spies and surveillance systems wherever they can, and rewriting many of the laws to keep wizards down. Harry ponders how much influence he actually had over the war (the contact will reveal others were planning to help the Society of Gilmour if he wouldn't) while Eve proclaims her disgust for how things have turned out and blames him for everything.