In the reality depicted in What if (2nd series) #9, both X-Men, old and new, perished in their battle against Krakoa, leaving only Professor Xavier and ex-X-Man Beast, who took care of the Professor, due to his depression. When several weeks later, Count Nefaria threatened the world and none of the other heroes were available, the Beast used Cerebro to contact several mutants and teleport them to Nefaria. Among them was Theresa Rourke, who had just begun training the use of her powers with her uncle, Black Tom. Hearing about her late father from the Beast, Theresa decided to take on the codename Banshee, and she also remained with the new X-Men after Count Nefaria had been defeated.
Not much is known about the events that led to the potential future was shown during the Shattershot crossover. Ten to fifteen years later, a much more mature Siryn was still a member of X-Force, just as were Cannonball and Sunspot. The other members of the team were much younger than them. Both Cable and Banshee had been killed several years ago. Apparently at some point, X-Force had helped Shatterstar to overthrow Mojo, the mad ruler of Mojoworld, leaving Shatterstar in his place. However, he wasn’t the best leader either, trusting the wrong advisors and, several years later, X-Force had to return to the Mojoverse once more, to help their friend set things right once more.
In the reality depicted in What if (2nd series) #46-47, Cable assassinated Xavier, Jean Grey and Cyclops, taking out the X-Men’s heart and soul. One team of X-Men sought bloody revenge, leading to a mutant civil war with there being repercussions for mutants worldwide as humanity grew increasingly hostile. In these dark times, Magneto proved a rallying point for mutants. His forces grew and, finally, his army attacked the White House. However, the president’s last act was to activate the Sentinels, one of which carried a nuclear warhead that detonated as soon as Magneto used his magnetic powers on the robot. With Magneto and his forces being killed in the nuclear blast, the world’s remaining mutants were easy prey for the Sentinels. Siryn was one of these few who were rounded up and put in concentration camps. However, Wolverine later bust her and several others out and, despite the incredible odds against them, they continued to fight for the mutant cause as the new X-Men.
Theresa’s counterpart from the Age of Apocalypse apparently never learned who her father was. In fact, she was living in an unnamed town in Kansas that was one day attacked by Apocalypse’s forces. All of the townsfolk were captured and shipped off to a testing facility to test them for mutant genes. However, Forge’s ragtag group of mutants attacked the transport to free the prisoners. When Theresa tried to warn one of Forge’s friends, Nate Grey, that he was about to be attacked from behind, she manifested her sonic scream for the first time. Joining the group as well, she adopted the moniker Sonique. Theresa and Nate quickly fell in love, but destiny had a much bigger fate for Nate in store. With both Apocalypse’s forces and Sinister coming after him, killing Forge’s group one by one, he eventually left to face Apocalypse all by himself, leaving Sonique in the care of their sole surviving teammate, Soaron. Later on, they were both brainwashed to serve among Sinister’s Six, but after being defeated by the X-Men, the tampering with Theresa's mind could be undone.
In yet another timeline, Siryn and Multiple ended up sharing the same fate, though it was an unpleasant one. Both of them had, at some point, been captured by Tullamore Voge and his slavers, who had turned them into Hounds. Apparently their former teammates were unable to rescue Jamie and Theresa from the slavers, either because they didn’t know of their fate or because they didn’t know where they were being held. Not to mention that with numerous of their arch-enemies working together to orchestrate The End of the X-Men, the followers of Xavier’s dream were too busy fighting for their very lives to even consider a rescue mission with unlikely chances of succeeding.