The number of fan theories that have come out from the Harry Potter series is pretty impressive. They play around with time-travel, meta-fiction and religious undertones. This one plays with the story in a very deep way.
Let’s start with Sybil Trelawney. Her prophecy regarding Harry and Voldemort is what starts this all off: that “either must die at the hand of the other, for neither can live while the other survives.”
Potterhead HPWombat found a very different way to interpret the prophecy. Either Harry or Voldemort must die at the hand of each other, that’s established. What if it their mystical bond stretches past that?
But when you give it more analysis, you see that it’s not as clear cut as you think. Most stories involving immortality don’t end well. It’s even sadder when you realize it’s Harry Potter in the middle of it.
In Harry Potter And the Deathly Hallows, after Harry dies from a Killing Curse coming from Voldemort, he doesn’t go immediately. In his time in the limbo that is the Kings Cross station, Dumbledore reminds Harry that “moving on” — AKA, dying — is the only way he will see the people he cares about the most.
Think about it: Before he dies, how many people had already died in his name that he won’t see again? Then consider his future. He loses the chance of seeing his kids and Ginny when they're gone as well. All this, in order to kill Voldemort.
That’d make for one heck of an epilogue. Imagine Harry, a century after the events of the books, Looking at his loved ones through the Mirror of Erised – the only way to see them that’s left. A sad ending, but powerful one.
There’s also an alternate version that saves Harry. It makes Neville Longbottom the immortal one in the story. That only applies if this is mixed in with the theory where he’s the Chosen One, not Harry. That’s a lot of speculation for one fandom, however.
This fan ending is beautiful in how it changes Harry radically. You don’t get a man that’s happily ever after, but a tragic hero. For all intents and purposes, this theory keeps him The Boy Who Lived, until the end of time.