The S3 buckets where HN is backed up to could themselves be constantly copied to other S3 buckets which could be the buckets directly used by an EC2 instance, were it ever needed in case of emergency.
That would avoid on-demand data transfer from the backup S3 buckets themselves at the time of failure.
The backup S3 buckets could also be periodically copied to Glacier for long-term storage.
That's for an all-AWS backup solution. Of course you could do this with (for example) another datacenter and tapes, if you wanted to... or another cloud provider.