What Nicholas has mentioned is correct, the Index Data for V1 Index are just flat files, which are also stored with the Data written to Disk Library.
In the scenario where a V1 Index Cache is lost or deleted, if a "Browse & Restore" or a Backup (Synthetic Full) requires the Index, it will recall the Index from Media.
- Note - however if the Index Cache is associated to a Storage Policy Copy writing to Cloud (this could incur additional cost due to recalling from Cloud) or Tape (this will require the physical Media in the Library).
In regards to load-balancing, when you change the Index Server (Backupset Level), during the next Backup, the required Index will first be retrieved from the previous Index Server, replayed into the Index Server (newly selected) and then it will continue to use this Index Server. Over time the old Index Server will age out content which has met retention.
The second method using the workflow is also another method to load-balancing the Index Server, but this will be distributing the load across the entire environment.
Usual Index Location - /IndexCache/CV_Index/2/<ID's of Client>