The first one is a hopeful: Mankind will, after having pushed itself to the brink of destruction in the Great War, survive and find its way (after overcoming some hurdles) back to its old greatness.
The second one is a fatal: After it reared up in the history of Fallout one last time, humanity will inevitably perish.
What do you think will happen? And what would be the better viewpoint from which future Fallout games should derive?
(PS: Is 'mankind' or 'humanity' actually considered neutral in English grammar?^^)