If a rocker panel isn't present on a truck like my C10, the entire cab seperates and the door no longer closes. On an Eagle its really just there to clip on a piece of plastic.
That's not the case. The rocker panel is structurally integral to the safety of a unibody car as it is part of what keeps the passenger cabin from deforming in an accident.
I've seen many people scrap Eagles because of hysteria. A hole in the rocker panel of an Eagle and moderate subframe rot is not a big deal on an Eagle. It's extremely over-rated. The chore of removing rusty bolts, not safety concerns, is what really makes a rusty Eagle more trouble than its worth. After 12 hours of struggling on a single bolt you'll be very tempted to scrap the car and use the money to buy a Jeep Cherokee. Eagles are considerably more difficult to work on than other vehicles of similar age, value, and capability. They are not a cheap and easy vehicle to own.
The AMC Eagle is literally a 1970 Hornet with new trim and a new crossmember. The 1970 version of unibody is much different than the 2012 version. The AMC Eagle was considered a very safe vehicle for its day because the solid bumper is bolted to weak links bolted to the body. In 2012 bumpers are plastic covering waffled plastic for crush zone. We're comparing apples and oranges.
What we typically refer to as the "rocker panel" is indeed aesthetic only on an Eagle. In the front the battery tray and inner fender wall is extremely important for structural integrity. It ties directly into a very stiff thick piece of metal running under the inside edge of the doorsill. That is the real rocker panel in an Eagle and it must be intact. The fenders are glorified mud flaps. Eagle fenders are aesthetic payload in the sense that they are big pieces of metal that bolt to the outside of the car's structure. You can drive around perfectly fine and safely with your fenders removed, you'll simply look ridiculous. Likewise a curved piece of metal was added outside of the stiff rigid body member for really no other reason than to look good and to continue the lines of the car from the fenders back. On a Hornet it is a loosely attached piece of trim. On an Eagle it isn't even visible and its just barely strong enough to rivet the trim clip to. That is the curved piece of metal everyone calls "the rocker panel." It gives as much protection and rigidity to the car as the piece of curved plastic attached to it.
In all of my high mileage Eagles here in salted PA the curved trim piece has disintergrated and has multiple holes throughout it. It's normal wear. That curved fake rocker panel's presence, however, has protected the real rocker panel behind it. I simply paint and protect the exposed metal inside and then fill the cavity with foam. I shave the foam and fill it in with waterproof and flexible "fiberglass hair" style body filler. It gets painted and the trim back on.
I have great respect for your husband, Priya. His knowledge and professionalism is obvious in his posts. His reputation and career would be in jeopardy if he allowed a unibody car to pass inspection with rocker panel rot because a vehicle safety inspector carries a degree of liability and an obligation to be professional. His perspective on a customer's vehicle will be different than his own. The question of whether a car is safe to drive is very different than asking if he has a professional obligation to condemn it.