On the very unfortunate night in the Potter manor, James Potter had been murdered by Tom Marvolo Riddle, famously known as Voldemort, the cheater of death. Lily Potter had died trying to save her only son, Harry Potter. He was on a mission to run from Thanatos, known as death, and be immortal. Voldemort had received a prophecy that a boy would kill him, he tried to find who the boy would be, and narrowed down two possibilities, Harry Potter and Neville Longbottom. Considering Neville to be not so much of a threat, he had gone for Potter. As he said for the killing curse for the first time (out of the three), he killed James Potter. As he raised his wand towards Lily Potter, the mother of Harry, and said the literally magical killing curse, “Avada Kedavara”, he felt something strange. He could not describe it. It was like a magical force pulling him towards the boy, who was only a few months old. He thought it was his greed to overcome his greatest fear: the fear of death. What he failed to realize was the fact that a love barrier had been created. As he shot the killing curse at young Harry, the curse rebounded and hit himself. But what if, instead of Lily protecting Harry, what would have happened if James had protected both of them?
First of all, it is important to know how difficult it is to perform a this kind of task. When James sent Lily and Harry and faced the Dark Lord, his main aim had been to kill the threat, or at least make him stay away and not sacrifice his life to save them… He thought that he could save both himself and his family. Another point is that his love may not be enough to save them both… As said by Dumbledore:
“Your mother died to save you. If there is one thing Voldemort cannot understand, it is love. He didn’t realize that love as powerful as your mother’s for you leaves its own mark. Not a scar, no visible sign… to have been loved so deeply, even though the person who loved us is gone, will give us some protection forever.”
Another point is that as said by the Harry Potter Fandom:
In order for the protection to form, the victim must be given the option to live, but consciously chose death.
But this is the universe of What ifs, so if such a thing occurred, there will be massive difference in the Harry Potter timeline and plot. The first major difference would be that Harry would not be with the Dursely’s and will still get the love and affection of at least one parent. In his childhood years, Harry and his mom would have become famous for evading the Dark Lord and would have always been on the run because of the Death Eaters. If they were not killed, Harry would go to Hogwarts normally because Lily would know that he becomes under the protection of Dumbledore. Now lets go book by book for the first three books:
First Book: There will be some foundation changes such Malfoy will despise him even more because he still has his mom. He will also message his mom regularly via an owl… But it could be that it is not Hedwig due to the fact that Hedwig was a gift by Hagrid and since his mom is alive, she would be the one to take him to Diagon Alley. Which means he may not be that close to Hagrid as he is in the book… This could result in Hagrid not spilling the beans…
Second Book: There will be a lot of changes in this book. What I think is that Harry and his mom both could have become parseltongue… I think Harry will tell his mom that he is hearing voices because she is close to him… But because of the fact that we have not delved deep into Lily’s personality in books, we cannot be sure how she would react to this… Could be she understands what the monster of the Chamber of Secrets is and then tells this to Dumbledore, already making his a bit careful of his steps… I think that Dumbledore would try to make the timeline go like the normal one to judge Harry (by looking at his decision trends).
Third Book: When Sirius escapes the jail, Lily would be the first one to tell him that Sirius is actually innocent and is nothing like his reputation. She will tell him all about how Wormtail betrayed them all.. This will change the whole book and I will leave it up to you to imagine how this goes.
I am only writing this much because my thoughts further definitely are very different from yours (mine are pretty violent… Sneak peak: War starts in the fifth book) so this could be unpleasant to some of you… I have already tested this post with my friends and that is why am saying this…