The only way to restore the contents as far as i'm aware is to rename the DB files that EV Creates for offline vault to *.PST and reconnect them through outlook
the only problem with this is though it does not hold a folder structure so you won't know whether the items were sent items, inbox, a subfolder etc etc
as for what will happen next is if the archive id's and what not are all the same it will most likely keep it until you do a reset, as in Offline Vault it will not delete items out of the offline vault, even though its not on the server any more
Vault Cache on EV8 though is different as when it syncs it will look at the storage and find out whats not on the server any more and then get rid of it out of the cache the client has
What i would suggest is making sure you get a safe backup of everyones offline vault.
But theres no easy or correct answer to this other than trying to save the data from the harddrives by one means or another and getting DVSChecker to get it all back in to the db's
https://www.linkedin.com/in/alex-allen-turl-07370146