My use case would be small local tools that need to keep some state. Essentially anywhere a SQLite would be useful. I don't think this was designed to serve as a database to back anything more 'serious'.
It's not the data authority. It feeds in data from Kafka and structures it in an optimized way for querying. If a node dies then it can copy from another node and restart from an offset in Kafka. Kafka essentially works as a distributed write-ahead log (WAL).