Restoring files is an added feature which has tape and storage costs associated with it, so I wouldn’t say there is an ROI. You need to instill in your users that if the data is not backed-up they could lose everything.
If you are trying to get the ROI on users saving their data so that they dont have a dataloss, thats a business question. Each company will have a different value to their data. And the value will vary within the company based on the criticality of the data to that business. Eg, payroll data might be most critical to accounting, and sales orders might be most critical to order fulfillment. But, as a company, it might be that orders are more important than payroll. So, in case of limited funds, they may decide that the highest level of protection is needed for orders, and payroll is second to that.