Dana and Kevin discuss how they cannot change history. Why, then, does Butler send Dana back in time, the driving narrative force of the novel? In terms of not altering history, could Dana have chosen not to save Rufus?

If Dana hadn't insured that Rufus stayed alive there wouldn't have been a future, at least not for her. Her life depended upon his survival; had she decided not to save him in his present, she'd never have a true present of her own.