Magical Britain went through great upheavals.
How could it not? Many wizards suddenly became Squibs and Muggles.
In truth, their numbers were smaller than they seemed at first glance. However, the backlash from the oathbreaking of the Minister, who had sworn on behalf of the citizens who entrusted him to represent their interests, affected the most active and visible segment of the population. This was primarily the Ministry workers who had replaced the regime after the Dark Lord's tyranny. The indifferent and inert rural backwater remained untouched and just as backward, but who cares about them?
As a result, the Ministry's ranks thinned noticeably. Those who questioned what magic meant to them and defined their answers received outcomes accordingly.
Many Muggle-borns became Squibs, and some half-bloods as well—those for whom magic was just an amusing addition to the worldview instilled in them during childhood. All the werewolves who wished to become normal humans turned into Muggles. The new Ministry leadership, installed during Kingsley Shacklebolt's rule, lost their magic since they were the primary group on whose behalf the pact had been made. Along with them went the progressive members of the Wizengamot, who had replaced the convicted and repressed.
The country was descending into literal anarchy. Eventually, the remaining Death Eater faction took power once again, as their opposition had essentially destroyed itself.
Britain, aware of Shacklebolt's role in the magical cataclysm, sighed in relief.
Despite the events of the past year—tyranny and persecution—the majority of people didn't oppose the new regime. The Dark Lord was gone, and for the average wizard, it didn't matter who ruled, as long as they weren't disturbed. Politically, the nation regressed a century, back to the days when the "Sacred Twenty-Eight" held power.
The Minister's oathbreaking echoed even in Hogwarts. Headmistress McGonagall became a Squib. She lost her position but remained at Hogwarts as a History of Magic professor.
Snape, caught between worlds as always, lost most of his magic but retained the ability to brew potions. Waving a wand was unnecessary for his craft, so he continued brewing for various apothecaries and shops. His wife, Lily Snape, retained the meager remnants of her magic, which had almost abandoned her after divorcing James, and remained a weak witch. Chubby little Harry didn't care about anything, so the cataclysm didn't affect him. However, the Boy-Who-Lived became the Boy-Who-Caused-All-This-Mess, so Lily kept him away from other wizards for fear of vigilante justice.
At St. Mungo's, Hermione Granger died despite showing signs of recovery. Once she became a Muggle, her injuries became incompatible with life.
Neville Longbottom visited Luna Lovegood in the hospital. When the regime changed and Luna was released from the psychiatric ward, he married her.
Dumbledore retained his magic. He never valued the magic of others, but his own, as it turned out, he cherished. However, he faced another problem—his entire body became covered in stinking, festering sores.
Dumbledore had to abandon public life.
In the Weasley family, only Arthur became a Muggle. He lost his job and, along with Molly, became entirely dependent on Percy, who managed to retain his position in the Ministry and even continued climbing the career ladder under the new regime. The older brothers, who hadn't supported their parents financially before, didn't start doing so now. Ron was incapable of earning money, Ginny never had enough for new clothes, and Fred and George were sentenced to a year in Azkaban. Percy was the sole breadwinner.
Ron married Lavender. He didn't work and simply lived off his wife, who had opened a fortune-telling salon with Parvati.
Ginny became a professional Quidditch player. She repeatedly tried to get married, but something always went wrong—even with Dean Thomas. Many were eager to sleep with her, but no one wanted her as a wife.
After leaving St. Mungo's, James went to live with Sirius and soon found work with the goblins. Together, they cleaned up Grimmauld Place and lived happily until James needed his own place. His friends had settled down and gotten themselves steady girlfriends. The path to the memorial in Godric's Hollow had long grown over, and the ruined house was beyond repair. So, James and Sirius approached Dumbledore. How they convinced their former leader remains a mystery, but a cottage in South Wales ended up in James's name. For weeks afterward, Dumbledore wore an expression of profound sorrow.
Naturally, they cleaned the traces of their spells from their wands.
Remus Lupin became a Muggle and had to leave the Greyback's Hollow. He didn't work harder or live better. Without the excuse of his furry little problem, he became an ordinary, gray, impoverished failure. James and Sirius didn't remember him.
What about Arcturus?
Yes, he gathered all three Deathly Hallows but never used them again. He also forbade his descendants from doing so.
He finally told Daphne the truth about himself. Daphne wisely decided that no one needed to know this truth and didn't even share it with her parents. She firmly believed that even if her Arcturus was indeed the same Harry from Hogwarts, nothing would change.
Six months later, they married and lived happily. They had children every two years, delighting Kreacher, until they decided to stop at the magical number five. Three boys and two girls—what a perfect number.
Arcturus rekindled his friendship with Neville, and their families regularly visited each other. He never reconciled with Draco, and their relationship remained formally polite.
Arcturus never admitted to Sirius that he was his father. Instead, he maintained warm familial ties with his adoptive father, Joshua Travers, and Joshua's new family, formed after the country stabilized.
Indeed, all the former Knights of Walpurgis started families. Even Augustus. Even Antonin.
After all, the continuation of the bloodline—the continuation of magic—was so important.
At twenty-one, Arcturus took a seat in the Wizengamot, and at forty-one, he became its Chief Warlock.
He lived a long life and died in old age, surrounded by his grandchildren and great-grandchildren.
In the history of magical Britain, he was remembered as a fair and wise judge.