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.