Well corporations that handle sizable amounts of data typically back up everything regularly as part of a standard operating procedure. If a hack steals everything and erases everything to the point of zero recovery, then the hacked company is either completely and utterly incompetent, or the "hack" was internal. I would find the latter scenario infinitely more likely in this case. Regulators are going to be way up in their ass either way.

That being said, I don't think it's going to be a problem of proving how much belonged to you as much as them paying out the said amount.