MySQL Cluster Steps To Recover Data If Catstrophic Failure Occurs
MySQL Cluster checkpoints and logs in-memory data to disk (assuming you leave the default of checkpointing on). As these are streaming writes, fast HDDs are very efficient to handle this activity. Also, all updates are synchronously replicated between data nodes in a node group, and these can be split across data centers using multi-site clustering:
https://blogs.oracle.com/MySQL/entry/synchronously_replicating_databases_across_data

So there are multiple mechanisms available to protect data

HTH!
Mat