In "Harry Potter and the Prisoner of Azkaban", Hermione was able to go back in time to change present. Does this allow for the resurrection of any character? There's one character in particular that I'm curious about:
Voldemort is dead now, but he was the connecting thread throughout the series. I would like the series to be continued, which I think means the return of He-Who-Must-Not-Be-Named.
Is it possible to bring back this character using the Potter universe version of time travel?
From "Harry Potter and the Prisoner of Azkaban", Harry Potter-verse time travel doesn't seem to change time, but rather bend it into a knot, causing stable time loops.
I.e.: Time travel can make things happen but not undo things that have already happened.
Technically, I think it may be possible under the time-travel model being used in the Harry Potter universe. We could have a situation where
Voldemort
actually came back in time from 2030 or something, and it was the time-travelling one that
Harry killed,
while the original one is in hiding somewhere.
As Oghma points out, JK Rowling has spoken against writing sequels, but authors have gone back on their words before.
I believe this wouldn't work for the following reasons.
The prediction that the chosen one would defeat aforementioned person, which is fulfilled in the events of the books.
The horcruxes were all destroyed, leading to his defeat.
If a time loop occurred that brought him back, time would cause the chosen one to defeat him again, fulfilling the prophecy in a different way.
If there was an additional horcrux, or one of them wasn't destroyed, it would change the events of the end of the last book.
The only example of time travel in the Potter universe that we see are the Time Turners, which were all destroyed in the attack on the Ministry of Magic.
If we assume that Time Turners are not banned from production, or that one could be made in the future illegally, then no, this would not work at all, based on how the Time Turner works.
Time Turners allow a wizard to travel backwards in time. They do not allow the wizard to travel forwards. While a wizard could possibly travel back to a time when Voldemort was still in power, it's strongly implied bu the events with the Time Turner in Book 3 that they could not effectively change past events as they were seen - and Harry was most certainly present for the death of that character.
More importantly, if they did alter events as you suggested, if it were possible, this would change the ending of the book - it would no longer be the ending that J.K. Rowling wrote, but an entirely different ending and an entirley different book, because as I stated before, time turners cannot bring a wizard forward in time.
Finally, it would be highly inadviseable for any wizard to do this anyway, since as Hermione says of her own time turner, going back any further than 24 hours could cause dementia or insanity. To say nothing of the inadvisability of bringing that character back from the 'dead'.
In short; Time Turners are gone, they couldn't bring a person forwards through time if they wanted, it would change the ending of the book completely, and it would be incredibly dangerous for the wizard attempting it.
The entire plotline of Harry Potter and the Cursed Child is based around the possibility of using a time-turner to try to resurrect Cedric Diggory. The play's protagonists, Scorpius Malfoy and Albus Potter achieve this with spectacular success but also ...
... change time to the point that they also accidentally resurrect Lord Voldemort and completely alter the timeline to a crapsack world with mudblood 'death camps' and public burnings of rebels and traitors.
It is, perhaps also worth noting that at the end of the play history has been restored so it's not actually a permanent resurrection.
Prisoner of Azkaban is the classic source for how time travel works. In the original timeline Harry sees someone cast a patronus and thinks it is his father:
For a moment, Harry saw by its brightness, somebody welcoming it back... raising his hand to pat it... someone who looked strangely familiar... but it couldn't be...
During the time travel, Harry realizes that he had actually seen his future self cast the patronus:
And then it hit him — he understood. He hadn't seen his father — he had seen himself —
Then in the time travel he actually casts the patronus:
Harry flung himself out from behind the bush and pulled out his wand.
"*EXPECTO PATRONUM!" he yelled.
This is exactly what had occurred in the original timeline. Harry, in fact, tries to explain this to Hermione:
"I knew I could do it this time," said Harry, "because I'd already done it.... Does that make sense?"
What we see from here is that the events in the time travel did not actually change the original timeline — they were the original timeline. Harry was originally saved from the Dementors because someone in the future went back in time and saved him. Buckbeak was originally saved from the execution because someone in the future went back in time and saved him. Harry didn't get kissed by the Dementor and then undo that by going back in time. Buckbeak didn't get killed and then have it undone via time travel. The original events happened originally in accordance with the effects of the time travel. In short, nothing actually changed — and nothing can change.
Therefore, it would be impossible to bring someone back from the dead via time travel. If the person would be saved via time travel then he/she would never have actually died in the first place; if he/she did actually die in the first place it means that no one went back in time to save them.
More generally speaking, there are several references to the fact that there is no way to bring back the dead via magic. In the end of Goblet of Fire we have the following statement:
"No spell can reawaken the dead," said Dumbledore heavily.
In his notes to "Babbity Rabbity and the Cacking Stump" Dumbledore writes:
As the eminent wizarding philosopher Bertrand de Pensées-Profondes writes in his celebrated work A Stdy into the Possibility of Reversing the Actual and Metaphysical Effects of Natural Death, with Particular Regard to the Reintegration of Essence and Matter: 'Give it up. It's never going to happen.'
In his notes to "The Tale of the Three Brothers" he similarly writes:
As I have already noted in the commentary for 'Babbity Rabbity and her Cackling Stump' we remain incapable of raising the dead, and there is every reason to suppose that this will never happen.
After leaving Xenophilius Lovegood in Deathly Hallows Hermione states:
"No magic can raise the dead, and that's that!"
If the dead could be raised via time travel, that would certainly bear mentioning. The unequivocal assertion that raising the dead is altogether impossible seems to indicate that it can't be done even via time travel.
