Minor Description
Having the DELETEREPLICA delete the index is scary for some situations, especially ones in which the operations people are taking more explicit control of the topology of their cluster. As we move towards ZK being the "one source of truth" and deleting replicas that then come back up, this is even scarier.
I propose to have an optional flag onlyIfDown that remove the replica from the ZK cluster state if (and only if) the node was offline. Default value: false.