I agree with you that data integrity is a huge problem. I believe local backups cannot be trusted. We all know that backups also can fail. Every SNO would use a different backup application, a different schedule etc. So the data coming from a backup is in a total unknown state.
The only solution I could think of is to download the entire node data from Tardigrade network and make the SNO pay for it like a regular customer. Of course escrow could be deducted.
Maybe escrow should be held indefinitely up to the amount that covers the cost of recovering the amount of space the SNO is providing.