As a fan of Harry Potter and the world that J.K Rowling has so lovingly crafted I've been mulling this thought over for quite a while now - what would have happened if Voldemort had won?
This is of course going from the assumption that it is not in an alternate universe/multiverse where Neville Longbottom will step up the chosen one. So, let's imagine what would happen if during the battle of Hogwarts when Harry goes into the forest to confront Voldemort, he does not drop the Resurrection Stone and keeps it upon his person. And also that he chooses not to come back while in Limbo chatting away with Dumbledore.
Harry Potter is dead.
Voldemort has the elder wand. He finds the Resurrection Stone and Invisibility Cloak on the body of his nemesis and keeps them, ignorant of their importance for the time being, then continues his display in front of those who were opposing him. He accepts those who submit and slaughters those who continue to rebel. Proclaiming himself the most powerful wizard in the world, he ties up all loose ends and seats himself as ruler of the wizarding world, with his loyal minions in positions of power. First in Britain with Hogwarts and the Ministry of Magic, and with no one to directly oppose him he extends his reach beyond across Europe, America and eventually around the world. He can now afford to be patient and allow his minions to take care of this regime change. While this happens he becomes curious as to why Harry had kept one of his horcruxes and looks further into this, discovering the legend of the Deathly Hallows and that possessing these makes him the master of death. The Elder Wand has submitted to him as he has dispatched its last master and the others submit recognising him as the last living descendant of the Peverell brothers.
Mad with power he concludes that he is, for all intensive purposes, a god.
This theory comes from the idea that gods and goddesses of the ancient world were power-mad wizards and witches, much of them interpreted by muggles. To me the Greek Gods definitely fit this bill. Egyptian Gods sounds though they could have been animagi or metamorphmagi, which is where the animal heads came from. The metamorphmagus trait could have been much more common in ancient times. The power hungry witches and wizards using their powers and fear to establish cults to themselves, but not being true gods they were still unable to evade an inevitable death.
Back to Voldemort.
He believes he is immune to death and an all powerful being. Not content with just ruling the magical world, he plots to also take over the muggle world. This could be achieved with surprising ease, influencing or corrupting those in positions of power and forcing any resistance with the Imperious and Cruciatus curses or killing them and replacing them with his own people. Naturally this would start with Britain as it would be easier for him to hold and his influence would spread across the world, making displays of power to prove that he is almighty.
By this point it is likely that he would have repressed and regressed any technological advancement from the muggles to reduce the likelihood of rebellion, or rather his minions would have. Given his arrogance and that he now believes himself a god I'd imagine he would not concern himself with something so trivial, however the Death Eaters and others loyal to him would need to ensure themselves to be untouchable as they are not immortal.
Of course his immortality is only theory at this point. While the life expectancy of wizardkind is much longer than that of muggles, there is still no guarantee that he can not die naturally as Ignotus Peverell did eventually. Although he accepted death, whereas Voldemort is less likely to. This could still take an exceptionally long time though, a life prolonged through many forms of magic, which would be longer than all other wizards.
That is where my thoughts end. My conclusion being that Voldemort would naturally declare himself an all powerful god. Well what else does one do when you are essentially the most powerful being on the planet?
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