StackSet AutoDeployment should be enabled and configured to retain stacks when member accounts are removed to prevent unintended deletion of stacks and their resources. Unintended deletions can remove critical security controls, logging, or IAM roles and cause service disruption.
For AWS::CloudFormation::StackSet resources, the Properties.AutoDeployment object must be present, with Enabled set to true and RetainStacksOnAccountRemoval set to true. Resources missing AutoDeployment, with AutoDeployment.Enabled set to false, or with AutoDeployment.RetainStacksOnAccountRemoval set to false will be flagged.