Up until the point that parts are no longer available, or so rare that their cost is prohibitive, it's almost certainly cheaper for him to keep the car than buy a new one. This also includes the fact that he does almost all the repairs himself, so it's also a hobby for him. He's also cannibalizing spare parts from several other salvage cars he has acquired.

A new car has so much depreciation in the first couple of years that it's a terrible idea for most people. Buying used cars and either maintaining them or just driving them into the ground and then buying another used car is almost always cheaper.