I recently ran into this readable article about AV safety cases by Thomas & Vandenberg from 2019. While things have changed a bit, it still is a reasonable introduction for anyone asking "what exactly would an AV safety case look like."
A real industry-strength safety case is going to be complicated in many ways. In particular, there are many different approaches for breaking down G1 which will significantly affect things. On the other hand all the pieces will need to be there somewhere, so choosing this high level breakdown is more of an architectural choice (for the safety case, not necessarily the system). We do not yet have a consensus on an optimal strategy for building such safety cases, but this is not a bad starting place from safety folks who were previously at Uber ATG.
Thomas & Vandenberg, Harnessing Uncertainty in Autonomous Vehicle Safety, Journal of System Safety, Vol. 55, No. 2 (2019)
https://doi.org/10.56094/jss.v55i2.46
(Uber ATG also published a much more complex safety case. However, I recommend this overview paper rather than that more complex safety case to get insight if you are just getting started.)
