NEO is fault-tolerant by design.
An object is written belongs to one partition but is written to multiple storage nodes, as much as the replica number requested if enough storage nodes are available. If a storage node crash, the others that handle the same partitions can take over the operations with no down time. A NEO cluster can face to storage crashes while there is at least one storage available per partition.
For the masters side, only one can be primary but secondaries are available to replace it in case of failure. Note that this require an administrator choice to validate the recovery informations found on the available storages nodes to prevent a restart from an old cluster state.