[Author here] The transactions and snapshots are still logged to disk. So if the cluster goes down and comes back up, each one just reloads the state. Until at least two machines are back up, we won't be able to serve requests though.

Not sure what you mean by ephemeral things. If you mean things like file descriptors, they are not stored. Technically the snapshot is not a simple snapshot of RAM, it snapshots through all the objects in memory that are set up to be part of the datastore. (It's a bit more complicated and flexible than this, but that's the general idea.)