Insurance companies have varying rules about "other drivers":
1. The vehicle owner's insurance covers any person who drives the insured vehicle;
2. The driver's insurance covers any vehicle that driver drives;
3. The vehicle owner's insurance ONLY covers those identified as an "additional driver" on the policy;
4. The driver's insurance specifically excludes driving any vehicle except the insured vehicle.
It varies dependent upon the insurance company, the driver's driving record, etc. (for example, a high risk driver may have a clause that denies coverage if the driver is driving anything other than the vehicle(s) on the policy)
Have him contact his insurance and ask about coverage if you are driving his motorhome; contact your insurance and ask about coverage if you are driving his motorhome. Then make a decision together based on the results.
I would start talking to him about potentially selling the RV. Even if he has rehab and is cleared for driving, is he going to want to travel in that RV with the memories (not to mention his wife's belongings)? Maybe suggest that he sell the class A and then, once he is back to driving, he could look at a class B or small class C?
My Dad had a hard time with the thought that he would not be driving again, but with some well-placed suggestions, he realized that downsizing his vehicle made more sense than keeping his 3500 diesel truck & 36' 5er. He actually enjoyed buying a "new toy". In the end, he never drove that new toy, but he didn't have that "I'm never going to drive again" depression at giving up the truck & RV.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)