The material in "Israel Endure Forever" is a somewhat different take on Jewish Continuity. I think the Rabbis probably "knew" what actions were needed, keeping halachah and doing Jewish study. But they needed reassurance that if the Jewish people didn't meet those demands, Judaism would continue. They showed great imagination in finding Biblical sources of support for Jewish Continuity.
We, on the other hand, fight over what we should do and have much less faith that it will work.