In an imaginary world where jelly beans taste like boogers and people actually sit still to watch a stupid game where all the players are flying around on brooms, there is one conceit that stretches credulity to its breaking point: the friendship between Harry and Ron. In real life, Ron would've turned on Harry after the 3rd book or so, and not for the reason you think.
In the books, the rift between Harry and Ron begins to develop because Harry has a crush on Ron's sister, Ginny. Fiction loves to pretend that men care so deeply about preserving their sisters' purity they'll kill their best friend if he makes a move on her (see Scarface for a particularly asinine example). This is old-fashioned, out-of-date thinking, though it would definitely alter the relationship permanently.
The real reason Harry and Ron's friendship is the most unrealistic part of the fantastical Hogwarts saga is this: No guy stays best friends with the same dude from ages 12 through 21 (or however old they are when the story finishes). There's a simple reason for this: One guy always matures faster. When you have that growth spurt and start realizing how much fun it is to try to get girls to sleep with you, you can't be seen hanging out with the dude who still looks prepubescent. In real life, Ron's voice would've dropped first, and he'd be picking on mudbloods with Draco Malfoy in no time. He'd probably pull down Harry's pants in front of all the girls and laugh as Crabbe and Goyle dumped him upside down in a trash can.
Then, since Harry still hasn't hit puberty, he'd have to go make friends with the lowliest social class: other kids who haven't sprouted yet, or kids even younger. He'd probably still have Hermione as a friend, since nobody likes her anyway, but they'd be joined by scrubs like Neville Longbottom and Luna Lovegood: the weird and pathetic.
But Harry would still grow up eventually. And when he did, his quest would not be to stop the Dark Lord or whatever, it would be pure and simple revenge. He'd probably still date Ron's sister (specifically to break her heart), but he'd be training and honing his skills simply out of hatred for all Weasleys. Voldemort? Who cares? Killing a guy's parents is one thing, but the wounds suffered from social humiliation in adolescence burn longer and deeper.
So the final chapter would be all about how the Death Eaters come back into power, and Harry's one of them, and he kills Ron while Snape nods in silent approval, his transformation into the new Dark Lord complete. I mean, what teenager has the ability to see beyond his own selfish perspective? Fight evil, save the muggles? No. I see him taking the easy way out 9 times out of 10. If you disagree with me, you, like J.K. Rowling, have never been a teenage boy.