Re: Dedupe
"...If those physical blocks die"
Maybe still a case to be had for tape backup?
Even better hey, as you said "multiple physical copies of the data", why not have those physical copies on different media. Disk only backups (inc traditional backup, CDP style, replication etc) is not the only option, expensive and often unnecessary, having one full (backup) copy + logical copies on disk is then maybe a reasonable option, with additional full copies found elsewhere.
While on the subject, why keep old backup data on disk at all?