Sincedb and ES unreachable

What happens to sincedb if I get this warning?

[WARN ][logstash.outputs.elasticsearch] Attempted to resurrect connection to dead ES instance, but got an error. {:url=>"http://localhost:9200/", :error_type=>LogStash::Outputs::ElasticSearch::HttpClient::Pool::HostUnreachableError, :error=>"Elasticsearch Unreachable: [http://localhost:9200/][Manticore::SocketException] Connection refused (Connection refused)"}

Does LS discard lines or not if ES is unreachable?

I've LS 5.4 and ES 6.x

Thank you.