Honestly, I'm not sure Oni has any ideas on how he's going to give the game an ending.
Pretty easy; decide on a day the game is ending, say 100, and then do a timeskip 5 years foward depending on main girl, with cameos from other conquests
No one : Back to human life(House of M?)
Rogue : Krakoa, part of the backup for the 5(Biokinesis focus)
X23 : War against Magneto, part of Xforce(Power Nuller focus)
Emma : Hellfire Academy, Stepford Cuckoo harem(sexual favor trading focus)
Jean : Casualty of the rise of Dark Phoenix/killed by Madelyne Prior
Kitty/Storm : Sentinels?