Kibana will make requests to the node at elasticsearch.url, and that node may end up talking with other nodes to retrieve data. Running an elasticsearch coordinating node on the same machine(guide) is currently recommended for balancing. If that node does goes down then correct, Kibana will go down with it.
Kibana doesn't support talking directly to multiple elasticsearch nodes now, we have an issue for tracking it here that has some suggestions. You could put a load balancer between kibana and elasticsearch, or have multiple instances of Kibana pointing to different nodes with a load balancer in front.