While this article leaves it ambiguous, the incident status report[1] makes it clear that customers can expect an actual postmortem:

"We will conduct an internal investigation of this issue and make appropriate improvements to our systems to help prevent or minimize future recurrence. We will provide a detailed report of this incident once we have completed our internal investigation. This detailed report will contain information regarding SLA credits."

[1] https://status.cloud.google.com/incident/cloud-networking/19...