As long as a majority of the servers are available, the ZooKeeper service will be available.
How do I size a ZooKeeper ensemble (cluster)?
A 3 server ensemble (you need to jump to 3 and not 2 because ZK works based on simple majority voting) allows for a single server to fail and the service will still be available.
How ZooKeeper Works
ZooKeeper runs on a cluster of servers called an ensemble that share the state of your data. (These may be the same machines that are running other Hadoop services or a separate cluster.) Whenever a change is made, it is not considered successful until it has been written to a quorum (at least half) of the servers in the ensemble.
the problem is that until the conflict is resolved, that document is not accessible.