Those rocker panels are important, but your car is in no danger of sagging into a taco. The shape of the floor pan makes a ridgid structure in the same way that sea containers with corrogated sides are more ridgid with less material than they would be with smooth sides. This is why a continuous frame rail isn't necessary. Technically we don't have a frame, but we have subframes in the front and rear. Many of us write frames when we mean subframe assembly. Its as sinful as writing trans to mean both transmission and transaxle.
Your car looks in much better shape than most of my rescue efforts. The rocker panels are a common rust issue on all sorts of cars, so it does have aftermarket support. JC Whitney has sold weld in rocker panels for Eagles. They cost about 75 dollars and I would expect a shop to charge several hundred dollars to restore your rocker panels to new condition. Most cars need them to be totally restored because they're externally visible, but we as Eagle owners are blessed to have strategic plastic molding that covers them all up. You have the option of making a crude repair with angle iron and then slopping a piece of pipe and bondo together for the rest. As long as the metal retaining strip ends up near where it started, the plastic will hide your dirty little secret.
Your rockers look to have too much gone to get away with it, but most people with several holes still have the option of filling the cavity with spray foam and then applying fiberglass hair (it stretches and is waterproof, so its highly superior to regular bondo) over the rough foam surface. That is all it takes to pass a safety inspection in PA. My Jeep Cherokee failed for a hole in the rocker panel and passed before we even bothered to cover the exposed foam. Most of us have heavily abused Eagles without intact rocker panels and suggesting that a car will break in half without them is just assuming the worst. Its up to you how conservative you want to be and how much time and money you want to spend.