Draco will show up on Harry's doorstep in Book Seven begging. For help. Yes. Help. That's it. Harry will hold a grudge at him for all of five minutes until his obsession with Draco's sleek blond hair overwhelms him and they spend the next six months gallivanting about Great Britain looking for horcruxes and testing out all the places it's possible to shag in public under an invisibility cloak.
Rosie will get so sick of Sam pining for Frodo that she eventually says to him, "Look, it's getting late, why don't you just go ahead and get on the friggin' boat already?" Frodo will spend about two seconds being weirded out that his lifelong love now reminds him of his Uncle Bilbo before deciding that as long as Sam can still cook it's okay. They spend the next 200 years staring soulfully into each other's eyes before one of the elves suggests they get a room. The slowness ultimately works to their advantage and they eventually discover that tantric sex is even better than that whole ring addiction.
So one day pretty much off the cuff Dom will be like, "So, why don't we just do that whole dating thing for a bit and see what all those fangirls are on about, then?" And Elijah will be all, "You're crazy. Why not?" And then they'll shag and cuddle and have pillow fights and go shopping together and kiss each other on MTV specials, and the world will, astonishingly, be just about the same, if a little bit more fun.
Elizabeth will surprise Will by having Jack over for dinner unexpectedly the next time he's in prison town, and threesomes will ensue. Elizabeth will top.
Wilson will get divorced for the third time and move into House's apartment temporarily. House will routinely throw things at his head in a reflex attempt to drive him away, but he lets Wilson put his feet on the sofa so Wilson really won't mind so much. Eventually House will figure out Wilson is never going to leave which is basically perfect, so he's all in all not too unprepared for the night they rent porn, get drunk, and wank each other off. Wilson's reaction the next day will be "If you were going to seduce me, couldn't you have chosen something more romantic than Deep Throat? Why not Lord of the G-Strings?" House will beat Wilson with his cane, and they will live happily ever after.
Ryoma won't so much follow Tezuka into the pros as surpass him and everyone else immediately, but when he plays Tezuka in their first pro match together it's the most thrilling thing he's ever experienced and his heart will clench at the look in Tezuka's eyes at the handshake. Ryoma won't know much of anything at that point besides tennis, but he does know that when he wants to learn about things, he looks to Tezuka, so things click in his head very quickly after that. He'll have Tezuka at his first low growl of "Buchou," and Tezuka, who's always been better at showing by example than telling, will have Ryoma several times over. And then they'll understand each other, and Tezuka will continue his ongoing sort-of flirtation with Atobe, and Ryoma will kick everyone's ass at tennis and think sex with most people is sort of boring in comparison, and they'll keep coming back to each other, over and over again, until they don't even need to ask for the keys to one another's apartments, and until gradually they only need one place with a tennis court. They'll only talk when they need to, and Ryoma will gradually realize that he's just as starstruck by Tezuka as he was at Seigaku, only a little bit deeper. And he'll be glad Tezuka isn't so stupid and sentimental, and stubbornly refuse to count the times when Tezuka slips his arm around Ryoma for no reason. And it'll stay that way as long as tennis keeps them together, and until tennis brings them together again.
In lieu of emo teen angst, Touya, directing his hormones at Go, will start to panic that Shindou is moving beyond him, and that Shindou might find another rival he likes just a bit better than Touya, and then he will feverishly play Go at all hours of the day and night, because it's unacceptable that Shindou should ever deign to throw him over for anybody else. Then Shindou will have some sort of comically disastrous first date with a girl, and Touya will have to face the possibility of a whole new rival he isn't prepared to defeat over a goban, which will inspire him to new, bold heights of bravery in which he screams at Shindou recklessly about Go and girls and treachery and end with snogging Shindou senseless and shagging him dizzy. Hikaru will go "Oh" and instantly become as addicted to sex with Touya as he is to screaming and Go matches with Touya. Touya's instinctive jealousy over Sai will evaporate upon learning that Hikaru will never have an opportunity of comparing them in bed, and then he will tuck Hikaru in his back pocket and keep him there for the rest of their lives.