I know what Hanlon's razor is, and I can guarantee you FB Engineering knows what a rollback is and how to know whether you need one or not. I'm not sure where you're getting the idea that they're that stupid.
Would applying such a 'rollback' involve replacing facebook.com email addresses with the original external domain addresses in the contacts list on the devices affected by the write-over issue?
If so: Facebook have taken private data and placed it in a central location
Yes, a (hypothetical) "complete rollback" would involve replacing removed data. Sure, data privacy would be a concern, but it's beside the point that rolling this back would necessitate un-overwriting.
