Two managers in cluster - m1 active, and m2 passive
Remove m2 from the cluster.
Remove also the active manager (m1) from the cluster, and try to upload blueprint.
You'll be able to create resources, although the manager has been removed from the cluster.
Also, if you try to start a new cluster, or joining one (with m1), you'll get an error message that says "This machine is already part of a cluster", even if the cluster node list is empty.