This sounds like a big story, and the fact they got Tony Isabella and Gil Kane to work on it makes it sound even bigger (if only because they aren't the regular What If team). However, it's a fairly quiet affair that feels like it could have been an issue of Amazing circa that time. Yes, the status quo is changed, but not irrevocably so, and farther reaching consequences are not explored. The Watcher makes promises about that, but never makes good on them.
What If Vol.1 #24 (December 1980)
Based on: Amazing Spider-Man #121-122
The true history: The Green Goblin, having learned Spider-Man's secret identity, kidnaps Peter Parker's girlfriend Gwen Stacy and throws her off a bridge. Spider-Man catches her ankle with his webbing and snaps her neck (depending on the edit anyway... this is the Greedo shoots first of the comic book world). In the ensuing battle, the Goblin is accidentally killed by his own glider.
Turning point: What if Spider-Man had chosen not to use his web-shooters on Gwen?
Story type: Wedding Bells
Watcher's mood: Giant monster
Altered history: With a bit more caution, Spider-Man dives for Gwen instead of shooting neck-snapping webs at her.
They land in the water, and the Goblin thinks they've drowned. Mwa-ha-ha. On the docks, Peter gives Gwen mouth-to-mouth (no, that's not a metaphor) and bring her back to life. She's horrified to see he's Spider-Man (whom she blames for the death of her father), but he explains everything and it's fine. SO FINE, in fact, Pete makes the ultimate move:
She says yes, and he's off to beat the Goblin's ass. It's not a happy reunion either. Spider-Man starts mowing through Osborn's thugs, shouting death threats. Osborn realizes his destiny is to die at Spidey's hands, so he quickly mails the details of Spider-Man's secret identity to Spidey's "other greatest enemy".
Oooh, evil. Spider-Man catches up with him at Harry's place. Harry stands up to Spider-Man and it snaps his dad out of his madness.
Spidey falls for the oldest trick in the book: Tears. He leaves them alone to reconnect. Aww. And it's off to Aunt May's to tell her the news. The kids don't wait a year either, they get married right away. Now, who can tell me what Peter's very basic mistake here is?
He gives her a chance to back out, she'll have none of it and they are married. Cute. And now for the Spider-Man's other greatest enemy. If you were thinking Doc Ock, think again.
J.J.J. walks in with the Goblin's proof and some cops, wrecking the wedding and Aunt May's health in general.
Man, I can hear Mephisto sharpening his knives from here. Peter won't go with the police easily though.
Perhaps not the best move. I mean, couldn't Flash Thompson or Alfred Pennyworth put on the spider-suit and confuse the cops or something? The proof comes from a known supervillain, after all. That stuff doesn't stand up in court. But that's not Peter's karma. He's on the run with a new wife pining for him. At least, Jameson gets his just rewards, with his entire staff quitting on the spot and going to work at another paper.
Books canceled as a result: Spider-Man Loves Mary Jane, sorry about that.
These things happen: They already had when this issue of What If? hit the stands, i.e. the Gwen Stacy clone. Plus the clone in Amazing #399. Plus Arnim Zola's four Gwen clones in Deadpool. And then there's that time in a movie when Mary Jane was thrown off a bridge by the Green Goblin... and survived! Someone must've sold her soul to the devil to make it out of THAT homage.
Next week: What If Thor Fought Odin over Jane Foster?
My guess: She was always a sucker for eye-patches (Nick Fury also tries his hand).