How Replica from one node to another will move?

Elastic Stack Elasticsearch
1

I have a 3 node cluster with 2 master eligible and all are data node & ingest node.
Setting is 1 Primary Shard and 1 Replica shard.
I have one index "nginx-2019.09"

For example Node "A" is master node and haves a Primary Shard of index. Node "B" has a Replica of the index. Node "C" is idle as of now.

Suddenly Node "B" went down in the cluster, Master node decides to use Node "C" as a replica for the index. Now Node "C" have whole index date up to date.

After few days back Node "B" joins the cluster. My questions are

  1. Now again Node B will become a Replica or Node C will continue as replica?
  2. If Node C continues as replica, What happens to the replica data which Node B has?
  3. Else If Node B elected as new replica, all the data from primary shard gets copied to Node B and Node C data will be deleted?

Kindly clarify my doubt

2

If you have a three-node cluster then all three nodes should be master-eligible. If you have two master-eligible nodes then your cluster is not fault tolerant.

Node C will continue as the replica.

Node B will ensure that the data is safely stored elsewhere in the cluster and will then delete its own stale copy to free up the disk space for something else.