I think we need to account an environmental impact too.
Since FC have (currently) only a block rewards to storage providers and FC Blockchain uses the PoW, it has a high impact on environment.
Even if they implement more robust audit system and possibility to repair corrupted data sometime in the future, they still uses a replication as a reliability mechanism and PoW to have rewards.
See The Green Case for Storj
So I personally think that FC cannot be used for robust and long time living backups. It can be not only lost or corrupted, it also will harm the environment.