On the world you know, there was a time when Rogue, the youngest member of the Brotherhood of Evil Mutants fought and defeated the original Ms. Marvel aka Carol Danvers. Rogue's mutant power is to absorb a persons abilities and memories upon physical contact. With Ms. Marvel's powers and her knowledge about the Avengers she was able to fight them off long enough for her mentor Mystique to attempt to break their fellow members out of prison. As it turned out Rogue by accident had permanently absorbed Carol Danvers. Although she liked to have her powers of flight, invulnerability and superstrength, she was from that moment on haunted by the memories of the strong-willed Carol-personality inside her head. Eventually it nearly drove Rogue mad; her last chance was to ask Professor Xavier for help. Since then she developed into a valuable member of the X-Men and learned to live with her guilt over the years. But, ....
The classic fight between Rogue and the Avengers went as in your reality. Mystique broke her team members out of prison but the unexpected arrival of Jessica Drew (Spiderwoman) delayed their departure long enough for the Avengers to join the fight at the prison too. Pyro, Blob and Avalanche being overconfident thought they could take out the Avengers but lost and were imprisoned again. Mystique ordered Rogue to fly her and Destiny away, just in time, because the borrowed powers of Carol Danvers were already fading.
Carol Danvers
Rogue
X-Men
Earth
Two weeks later. A small starship emerges from hyperspace and immediatly heads for the sun's third planet - earth. It's lone passenger Wolverine scans the surfaces with longdistance cameras and is shocked to see the planet swarming with Brood. Like they always do, they strip a planet of all it's ressources. Almost all plant and animal life is killed or eaten away. Whole countries only show bare rock and bones. In tears Wolvie orders the computer systems to scan for human life-signs. Surprisingly the computer locates two - only two. Adjusting the camera Wolvie sees earth's last survivors : in the middle of San Francisco's Golden Gate Bridge are Ms. Marvel and Rogue - back to back fighting against overwhelming odds. Both look tired. Wolvie uses a long-distance transportation beam to get the pair out of this hell.
Decisions are quickly made; since the Brood are without any starships and trapped on the planet, Wolverine, Carol and Rogue target long-distance weapons for earth's nuclear plants, fire and quickly travel out of range. From afar they see earth go down in a big fireball. The trio decides to move on through the galaxy, defending other races from the Brood.
Often the seeds of victory in one universe breed defeat in another and so my ancient eyes are accustomed to witnessing as many tragedies as triumphs, like this time. But no matter which or where the world ... it seems there will always be "X-Men".
In the aftermath of the battle Carol awakes from her coma in San Francisco just as the Avengers are about to visit her. With them is Spiderwoman, the woman who saved her from drowning in San Francisco Bay. Here too Carol blames the Avengers for letting her down a few month ago, when she under mindcontrol accepted to follow Marcus to Limbo. None of the Avengers present realized that she was not going of her own free will, and she had to pay the price. In Limbo Marcus died and after many months alone she taught herself to master his devices. Eventually she found a way back to earth, but refused to contact the Avengers blaming them for her fate.
The Avengers listen to her with awe, all of them, especially Wanda, feel guilty about their ignorance back then; but nothing they can do is enough for Carol. Of course she understands that all of them are sorry but she now officially quits the Avengers fearing that they could let her down again.
After the Avengers left, only Spiderwoman remains. Noticing that both females have much in common she makes an offer Carol gladly accepts. A week later Carol signs the papers that make her Jessica's equal partner in their new "Drew & Danvers" private investigator's agency. With her espionage background and her superhuman powers Carol more than qualifies for the job, and of cource the agency becomes a succes; it's beautiful owner's are now local celebrities of San Francisco.
Mystique is really proud of young Rogue. Her first assignment and she held her own against the Avengers. That the three male teammembers got themselves caught back at the prison was their own fault she says. That is why she will let them stay in jail for some time to think about who's the boss of the Brotherhood of Evil Mutants. In the following weeks and months Mystique and Destiny continue Rogue's training and with each mastered task she grows more confident and gains more control over her abilities to the point of actually being able to touch without absorbing. (This Rogue lacks the psychological barrier that the Rogue of your reality set up after her accident with Carol)
Since Rogue here still is ground-bound and vulnerable, the three mutants lack some firepower. Instead of recruiting new members they develop into an undercover organisation. The world is full with possibilities for the mutant trio. Mystique can become anyone she wants, and Rogue can absorb knowledge, information and skills others would take years to aquire. Completed with Destiny's precognitive powers, the three women build one of the most powerful secret empires. They rename themselves to Sisterhood and completly forget about their former members.
Months after the incident between Avengers and Brotherhood, the X-Men, consisting of Storm, Cyclops, Nighcrawler, Colossus, Kitty Pryde and Wolverine, encounter the Shi'ar. Their princess Lilandra has been kidnapped and all evidence points to earth. Yet the X-Men discover that Deathbird formed an alliance with a yet unknown species called Brood. They had placed those false clues pointing to earth and were really behind the kidnapping. Of course the X-Men are able to rescue the Shi'ar princess, but Xavier receives some injury during the battle. While he recovers under Moira's care, the X-Men attend a ceremony on Lilandra's starcruiser. Unknown to them all the party is an illusion : instead of dancing and singing Shi'ar the hosts are the dangerous Brood. Their queen infects all the X-Men with her eggs and redirects the ship to her homeworld. Never before has she seen more powerful hosts. The eggs will hatch in time and the parasite will slowly but surely take over the host and transform into a Brood keeping all the special mutant talents of the host. As the X-Men become aware of their fate they decide to make their remaing lifes count - if they have to die, not alone. They'll take out the Brood Queen too.
If you remember how events turned out in your time, you'll know that the recovering Carol Danvers was among the kidnapped X-Men and infected as well. The Brood's tampering with her genetic structure caused her transformation into Binary. This unexpected and powerful ally is missing in this reality.
Of course the X-Men fight on and on, and eventually kill the queen, who reveals just before dying that another Brood egg was placed into Xavier. The battle took it's toll and the X-Men no longer have time to return to earth; the only one still in fightining shape is Wolverine, whose healing factor rejected the egg. All the others are slowly transforming. Storm commits suicide at the first sign of Brood elements. Kitty tries to phase the parasite out of her body and Kurt tries even harder teleporting without his implant, yet they fail. Wolverine puts them out of misery in their sleep and mercykills them, then he takes a small starship back to earth.
Xavier kept the evil influence in check as long as he could, but still weakened from his recent injury the outcome was undeniable. Finally it was no longer Xavier sitting in this wheelchair, it was a new Brood Queen. It's first victims were the new students Xavier conveniently assembled - the New Mutants. With Xavier's telepathy the Brood hit the jackpot, not only could the Queen contact former X-Men and other superheroes to lure them into traps to infect them as well; the Brood also influenced the inhabitants of Westchester to not noticing the space-insects living in their mids, until "Xavier" had an army of dozens of mostly super-powered Brood.
Then one night came the surprise attack, the "Beast" was placed inside the Avengers, the Brood started to infiltrate government, military, and foreign countries. Until most of humanity realized what was happening a quarter of earth's population was already transformed or killed.