 Un-manage should not fail when any one or few storage nodes are down

Un-manage flow is timed out and failed when any one or few nodes are down. RHSWA expects all storage nodes to be up while running the un-manage flow. If any node is accidentally removed or down then the only way to re-import the cluster is manually clear the data and restart all the services. Ideally, RHSWA should allow the user to unmanage the cluster when at least one node is up. 
