What If vol.2 #23 (February 1991)
Based on: Giant Size X-Men #1
The true history: The original X-Men land on Krakoa the living island and get captured by the monster. Professor X assembles a new team of X-Men who free their fellow mutants. After the dust settles, many of the original X-Men leave their spots for the all-new, all-different guys.
Turning point: What if Krakoa had not gotten the jump on the original X-Men?
Story type: Hockey Trade
Watcher's mood: Cross-eyed
Altered history: In this new reality, the X-Men send Krakoa spinning into space with Polaris' magnetic powers much earlier, obviating the need for Xavier to recruit a new team. Not only does the team stick together, but Beast even leaves the Avengers and comes home. So what of the X-Men that MIGHT have been? Well, Nightcrawler and Thunderbird (now Proudstar) get conned into attacking the X-Men by a Shi'ar posing as Eric the Red.
Nightcrawler escapes at the end. As for the old X-Men, they have to face pretty much the same threats the new X-Men did in our continuity, but there are differences in how they handle them. For example, though Jean Gray is all about sacrificing herself o bring down a shuttle from a Sentinel base in orbit, Polaris reminds her that she can do it easily with her magnetic powers. And so, the Phoenix Force is never attracted her way and never comes to possess her. No Dark Phoenix, no genocide, no death and return of Jean Gray. The X-Men just have to find a way to overcome threats originally handled by the Phoenix, that's all.
Other adventures do happen though, and the all-new, all-difference mutant concepts appear here and there. The Warhawk who infiltrates their mansion is now Colossus. They go to Africa to prevent Arkon from kidnapping Storm. And when they help Sunfire with Moses Magnum, the Japanese government also enlists the help of Canadian super-team Alpha Flight. And who's a member? None other than Wolverine! I guess he'll take any Japanese missions he can get so he can see Mariko.
Logan inspires Cyclops to ask Jean to marry him, but Hellfire Club trouble comes knocking before they can order the flowers. Of course, without the Dark Phoenix's influence, Jean isn't tempted to become the Black Queen. But speaking of the Phoenix Force, the X-Men are suddenly whisked away by the Shi'ar who want to destroy our sun, where the Phoenix has been hiding all this time. The X-Men ask for a few days to try and fix the problem themselves, and Cyclops' plan is to allow the Phoenix to take him over so that the Shi'ar can immediately kill HIM. Well...
So who is this shadowy figure willing to sacrifice himself for Cyclops/the universe? Here's a clue:
"Unglaublich." Yes, believe it or not (and I have trouble myself), it's Nightcrawler. He's been following the X-Men since he escaped from them and has seen they do good works. He eavesdropped on the plan to kill the Phoenix and decided to redeem himself for that time another dude tricked him into attacking the X-Men. He's the Phoenix for all of 2 seconds before the Shi'ar blow him up, leaving the X-Men depressed and Professor X expounding on how "no man is beyond redemption, no man." A fine speech for the likes of, I dunno, Magneto or, you know, Parallax, but a random mutant dude who was at best misguided that one time? I sure hope to hell he could be redeemed! The Marvel Universe is a harsh mistress!
Books canceled as a result: Depends. It's entirely possible that the revised first appearance of Alpha Flight would have led to their own series and from there, Wolverine's rise to popularity. However, the X-plosion of the late 80s and early 90s seems less likely when you consider that Uncanny was only a lukewarm seller before it made the big cast changes. It would have continued to plod through, month after month, without attracting much more of an audience. Imagine a world without New Mutants, X-Force, Excalibur, X-Factor and so on. Heck, it might even mean we'd have been spared DC's Sovereign Seven (Claremont no longer prized super-star) and quite a few early Image comics.
These things happen: All the X-Men who dropped out after Giant Size X-Men eventually returned to at least one of the X-Men books, and Nightcrawler is indeed eventually killed (in Second Coming).
My guess: Things would have gone down the Twilight.