I have been following this thread, and am very glad to hear your dad has returned safely.
May I suggest that you honestly evaluate his capabilities for driving a motor vehicle. We had an incident last year in which an elderly man killed nine people and injured 55 people when he mistakenly thought he was pressing the brake, and was actually pressing the gas pedal. From your descriptions, it sounds like your father may be nearing that point.
I know this is one of the hardest things a son or daughter has to do, but think about the consequences, because they can be much worse. Now the elderly Santa Monica driver has to live with knowing he killed and injured so many people. He is being prosecuted for manslaughter. I'm sure he is devastated, and certainly the families of those who were killed or injured are. There were warning signs about his driving abilities long before the Santa Monica incident, and no one did anything about it. The result was tragedy.
In some cases, you can report elderly drivers to the DMV, and they will mandate a driving test. It is probably better though, just to convince the elderly relative that it is time to give up driving. Try to setup alternate transportation for him. There are senior citizen transportation services in many areas. Taxi's are always available. Relatives driving them to shopping and other activities are another option. Being lost for two days may be a good starting reason to make your case.