Somehow, the original Stargate translation team manages to open the "Doorway to heaven" without Daniel, and avoid killing the Abydonians (AKA, everything goes more or less the way it did in canon, but with even more translation problems--maybe the military people are really good at Charades, or something). And then they head out into the galaxy to fight the Goa'uld, but with tons of comedy moments because their translators aren't Daniel, or even Daniel-trained.

Semi!sentient Hogwarts realizes that they're at war and vulnerable. To increase security, she starts requiring passwords to be changed every 90 days and contain at least one number, one capital letter, and one lowercase letter, and be at least 8 characters long.

Some time after they've parted on bad terms, Duncan finds one of Methos's old diaries. Remembering how many times Methos had intruded on him and trying to get a petty little bit of revenge, he sets about trying to read the diary. It's not as easy as it sounds: Methos switches between languages when he feels like it (and engages in polyglottal wordplay along the way), and Duncan doesn't know most of them, so he has to go out and learn them. Well...it's not like he doesn't have time, so that's what he does for a few lifetimes (and ends up making a reputation for himself). And when he can translate enough of it, he finds that the diary is essentially a list of Methos's regrets. Many of them are cryptic to Duncan, because Methos doesn't need to describe the whole situation to himself, and Duncan doesn't recognize what referents Methos did write down. Others are multi-page rants/essays. Some of them, Duncan can figure out that they're fictional; others, he knew enough beforehand to know that they're real.

Whichever Highlander movie in which they're aliens, but Methos won the Game, not Connor. Which is a bit more interesting now that I think about it: he'd still create the Dome, because he wants to keep Earth habitable, but other than that...I can't really see Methos being all "yay! Now I'll grow old!" as his Prize. So he'd still be young, and he'd still be living, and maybe a part of that group who broke in to check on the ozone...

Atlantis University thinkiness

They go in thinking that it'll be a long time before contact is reestablished, and act accordingly. Which means that from the beginning they know that they need more than just the expedition members and relatively easily combine with the Athosians. Politics means that not only the scientists are from multiple countries, the military are too. To simplify things a little bit, they rename the mass of them (so they're not marines or air force anymore) and make them do lots of training together to make sure they have skills and can understand each other (English speaking is a requirement, but depending on a foreign language in the middle of a battle? Best not to do it without lots of practice) which also helps clarify the chain of command and find personality clashes. Scientists do at least some training with the military, and stay at the same place with them for the duration of the long training even though theirs is shorter, to find issues *there*.

Shawn Spencer is a go-with-the-flow kind of guy. So when Lassiter misinterprets one of his visions/antics as a come-on and accepts, he goes with the flow. And he's used to relationships collapsing, getting dumped after a few weeks; so much so, that he's extremely confused when Lassiter doesn't break up with him, and doesn't break up with him, and doesn't break up with him...until Shawn finally gets used to it. And then he does. And Shawn has to figure out how to win him back, when he's only just realized what he had.

Muggleborns are quietly fed love potions targeted at purebloods and halfbloods, until they have their first pureblood child. By that point, the love potion has long-lasting effects on most of the muggleborns. For those who break free, they can get a divorce...but their spouse would basically get to keep everything, because a muggleborn is obviously less capable, etc. And the wizarding world hates divorce, so good luck finding or keeping a job in the wizarding world as the muggleborn instigator of a divorce.

Girl!Dexter. Her gender is just another reason Harry adopts her, but despite the statistics she still becomes a serial killer.

Although they're all adult and responsible now, Hermione's parents were the pranksters of their school growing up, and to be honest they're a bit disappointed that Hermione's so rule-abiding. But then she's falsely accused of a prank (or her parents think she's pulled off a prank, anyway), and instead of blowing up at her they're proud of her.

You know what plotline would translate well into the Harry Potter-verse? Oedipus Rex. There's a prophecy that he'll kill his dad and marry his mom (or maybe sister), so they curse him and abandon him in the muggle world. His dad...is a Death Eater, maybe? The wizarding world doesn't have the "marry wife of dead king to become the king" thing, though, so that'd have to be fiddled with. Maybe with the marriage law trope?

Of course Methos recognizes Andrew Wiggin as Ender--he's certainly got enough experience to recognize children once they've grown up. But whatever the Speaker for the Dead wrote, and whatever orders Congress gives him, he was on Earth throughout the war, and he won't do anything against the man who ended it.

(I guess he's captain of a ship that was at the planet when Ender got in trouble...gah, it's been so long since I've reread that I don't remember exactly how it went)