UPDATE: We are traveling in Montana and for some reason here, diesel fuel is about 10 cents cheaper a gallon than regular. I don't know if this is a temporary anomaly or a regular thing. In Georgia, diesel is about 20-50 cents more a gallon than regular. Regardless, you are looking at a decade or more to justify the cost delta with a diesel. And once all those "high mileage" VWs are reprogrammed to conform to emissions standards, their mileage advantage may disappear entirely, leaving owners with cars that cost more, but deliver the same or similar mileage as their gasoline counterparts. Maybe the class-action lawsuit will help,but I suspect the result will be a coupon good for $500 off a new VW - and millions for the law firm filing the case.
And yes, if you want to pass emissions testing in the future, I suspect they will check to make sure the software hack has been removed.... A massive recall is likely in the future.