I'm working on a fix
While discussing this upstream, it was proposed that a better solution would be to set up a load balancer for LDAP (which I agree with). A load balancer is better placed to determine if a server is down and act appropriately, whereas keystone doesn't have any inter-process communication or place to hold such state.
The documentation has been revised and published: https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/16.2/html/integrate_openstack_identity_with_external_user_management_services/assembly-integrating-identity-with-idm_rhosp#con-planning-identity-idm-integration_identity-idm