I think it would be more interesting if the Book of Fates was written in a somewhat more vague manner rather than explicitly laying out how everyone dies Death Note style.
Every scenario would then be a puzzle to achieve what the characters want while still technically fulfilling the relevant prophecies. The prophecies WILL be fulfilled and if you try to circumvent their obvious meanings and fail, either you get a Doomed Timeline or they just revert to the prophesied outcome in the most brutally efficient way possible. Either way it would be a bad end. On the other hand, just accepting your fate also leads to a Bad End (because obviously if you're fighting fate it's because yours doesn't sound too hot).
The Book would emphasize the most important, famous events a person participated in, their critical moments if you will. So those would be the ones you'd play out. Let's say someone was fated to "fall in battle against his most hated foe." Fall in battle is poetic language, but you can rules lawyer it to literal language - the character slips and falls, prophecy fulfilled and he gets to live!
... except he's dueling his most hated foe, who's just going to kill him anyway unless you carefully engineer the situation so that doesn't happen.
If you succeed in slipping someone free of the Book's prophecy, then their fate is no longer predetermined (except insofar as it intersects with someone else's fate), which allows you to recruit them to help you in later scenarios. But later prophecies would get more complex/harder to lawyer.
Eventually, you'd have enough people freed of known fate that you could challenge it directly (somehow). The final scenario would be finding away around the seeming invincibility granted the Divine Ruler by HIS fate, whatever that might be.
I'm not sure how the actual gameplay should work - some mix of point and click adventure game and visual novel leaps to mind.
