Most other systems that have a Historian have a built in tools to archive and restore history from saved files (Pi, WonderWare, Citect, Experion etc etc.)
IA Support have advised me that it can be done, but it is a very manual process.
Archiving out by partition/month with the ability to restore would be a great feature.
No doubt this is a technical hurdle due to the number of supported DB formats, but you have some clever devs!