Elasticsearch as a primary data store

Question

I've read a lot of posts on using ES as a primary store and whether it's a good practice or not. But nowhere I could find whether ES will fail the request 100% of the time when it's unavailable ?
What are the conditions in which ES can lose your data ? One of the conditions I found was nodes are down, but in this case the insert / update request itself will fail and the client can retry. What I am looking for is whether ES rest highlevel client will respond with 200 OK and internally lose data ?
Also if I don't need ACID properties, but need to be fault tolerant and have some protection against data loss. Is that possible with ES ? with replication ?

The articles or blogs that I've read so far are :

1. Using ElasticSearch as source of truth
2. How reliable is ElasticSearch as a primary datastore against factors like write loss, data availability
3. AWS Elasticsearch as a primary database