great fanfic, but as far as I can tell, completely baseless theory.
there are a few things I don't understand, and I don't know if you have something to back up what you're saying, or you just think it would be cool.
What makes you think Gryffindor's sword would deflect any blows Voldemort would first throw at Harry?
Have you realized Trelawney's average of true prophesies is one every fourteen years? I personally think her prophesy days are over, but I seem to be the only one who believes that, so I'll let it slide.
As much as I love Dumbledore, I do think he'll somehow sacrifice himself. But I have to wonder, would this give Harry the extra teensy bit of protection he needs to finish Voldy off? The only other time we know of someone sacrificing herself has left Harry with some pretty amazing protection.
I got totally confused on the "this happens a week earlier, but no one believes Harry" thing... What happens a week earlier? Why would Dumbledore, headmaster of Hogwarts, leader of the Order of the Phoenix, be hiding in his office for unknown reasons when Voldy has come to the school? Dumbledore believes everything Harry says regarding what happens, so I don't think "no one would believe Harry"... And I don't think Dumbledore would be inaccessable in times like these...
Harry runs at voldemort and slices down. But as soon as the sword touches Voldemort they are transported to Godrics hollow where two wizards are duelling. One is Salazaar the other is Godric.What they are seeing is a vision of what happened in the past. Godric runs at Salazaar and runs him through with the sword of Gryffindor. There is more talking and then harry runs at Voldemort again and they are both blown back by the force of the ensueing gusts of wind emanating from the poin of the blow. Voldemort is killed and then all the terrible things voldemort did were reversed and Harry meets his parents.
Total fiction. There's no reason to believe they would be transported to Godric's Hollow, no reason to believe we'd see Gryffindor and Slytherin fighting, and the ending, where everyone lives happily ever after is, in my opinion, the anti-Rowling...