Man I feel bad for your dad. I once blew the o-ring on my 2008 6.4 psd and it lost a lot of oil but I caught it right away. Left a big pool of oil under the truck. My advise to you is to not tell Ford anything at all. Just top it off with oil and drive it as long as possible. Start taking it to Ford for all the future oil changes and maint. Then right before the warranty expires, tell Ford whatever(it's smoking,using oil,knocking,vibrating,whatever), and hope that they fix/replace the motor. It may last a long time. Just depends how long he ran the motor after the oil was gone. Worst case is you will have to buy another motor. They can be found for as little as $2600 in some junkyards. Just my opinion.