Originally Posted by
Endsong
AvX didn't happen. Anything involving the Phoenix as antagonistic? It didn't happen.
Jean and Wanda would work together, using Hope as a catalyst, to reignite the mutant spark. The X-Men would probably come back together after this, given that they aren't about to be extinct anymore. Jean and Scott, despite rocky times, are still probably together. Jean stays in charge of the school, with Scott in charge of the X-Men proper. They'd probably take more of a stance like is currently happening in Ressurxion with Kitty, with the X-Men becoming heroes again. Charles is alive, but still taking more of a backseat.
The O5 don't come to the past. Bobby comes out on his own. Warren still "dies," and Beast still mutates. Jean would have been on the arc when the Incursion happened, and wouldn't have died at the hands of Doctor Doom - she would probably remember what happened as the Phoenix is an omniversal force. Ends up on both the X-Men and the Ultimates in the aftermath.
When the Terrigen bomb drops it would still take a while to realize what it is doing, but I think that the X-Men and the Inhumans can come to a more diplomatic end when it comes to how it was worked out. Scott and Madrox are still the first casualties, but Emma isn't driven to do what she did thanks to the fact that she and Scott weren't in love, and Jean isn't nearly as unstable to do something like that. She grieves, but she does so on her own, with her friends at her side. The Terrigen Mists are destroyed much sooner.
All in all, the MU would probably be a much better place if Jean had survived. So that's why she didn't.