This is likely to be Fassbenders and Jennifer Lawrence's last Xmen film. I can't see them signing up for any more given how both are likely to be huge A list actors soon.
J-Law is, but I think Fassbender doesn't have quite the same staying power. If that Assassins Creed movie makes money, and he proves he can pilot a profit, perhaps. But they also might just say the movie was profitable because it was assassin's creed.