The problem after 70 was total. The religion of Israel as the scriptures describe it is built around a Temple, a priesthood and a sacrificial system, and all three had just ceased to exist. What Johanan ben Zakkai did at Yavneh was to transfer what could be transferred and to authorise a substitute for what could not.
The enactments attributed to him are practical and specific: the palm branch is to be taken for seven days everywhere, as it had been in the Temple; the shofar is to be sounded at Yavneh when the New Year falls on a Sabbath, as it had been in the sanctuary; testimony about the new moon may be received all day; priests may pronounce the blessing without shoes. Each moves a Temple practice into the world that survived it.
The theological substitution is stated in a short exchange. Joshua, seeing the ruins, cries out that the place where Israel's sins were atoned for is destroyed. Johanan answers that there is another atonement as effective, and quotes Hosea: I desire mercy and not sacrifice. Acts of loving kindness take the place of the offerings.
One thing he did not do is close the canon. Nineteenth and twentieth century scholarship spoke confidently of a Council of Jamnia around the year 90 which fixed the Hebrew scriptures and expelled Christians from the synagogue, and Jack P. Lewis showed in 1964 that the received account rested on inference rather than evidence. The academy debated whether particular books defile the hands, which is a question about the status of individual books, not a canon-fixing session. The atlas holds the phantom council as its own entry precisely because it is still cited.