Logistically and morally your argument makes absolutely no sense at all to me, I'm sorry.
Without them, we wouldn't have our chance at all.
We would be in their same shoes if Sullivan had not convinced the Council to protect us instead of the Book. We would be in their shoes if not for that, so they didn't "fail" by any fault of their own. We were lucky. That is all.
Everything indicates that their Book disappeared when they did.
And can you live with yourself knowing that they are disappearing, dying, and that Augernon will eventually be institutionalized if we do nothing?