you can manage domain only from domain controller. If domain controller goes down it is not possible to manage domain from slaves. They don't have full copy of domain configuration.
WildFly has sort of failover mechanism. On slaves you would need to configure domain discovery which allows reconnecting to one or more alternate domain controller.
<static-discovery name="primary" host="192.168.0.1" port="9999}"/>
<static-discovery name="backup" host="192.168.0.2" port="9999"/>
backup can be one of other slaves which is started with --backup option which causes the slave host controller to create and maintain a local copy of the domain configuration.
When primary domain controller goes down, slaves with local copy of domain configuration has to be manually promoted to domain controller.