I keep coming across the sentiment that simply giving the Romans either better technology (medication), or better politics (abolished slavery, wealth redistribution) would avert the fall of their empire, but there were so much more that caused that fal l than any one answer. For instance, the plight of the poor was one of the motors behind the rise of the populists - the party of Julius Caesar. But the most neglected linchpin of them all is the environment itself, and how much the land itself degraded under the Romans. The Romans ran a very short-term centred economic system for the Mediterranean, where Pax Romana connected all of the resources of three continents together into one gigantic network, the likes of which had never been seen before. This is how the wealth of the city of Rome was created. But the Romans left the environment no room to recover, which is one of the reasons for why the late empire became less and less wealthy.
For example, the clear-cutting of forests lead to soil erosion and the subsequent lower crop yields, and that coupled with extensive goat grazing on the now clear-cut lands made regrowth impossible. That is not all though, the rich soils' nutrients did not simply disappear, they were swept away by rain into low lying wetlands, creating large amounts of malaria-infested swamps. And then there is the hunting of predators. Roman writers greatly approved of the practice of hunting down predators like foxes, and then also bemoan the fact that the population of disease spreading rodents like rats had dramatically increased. This is part of the reason why the late empire saw so many epidemics.
But Europe did recover after the Romans, even though it took us a thousand years to do so. (But I still want more great cats than the lynx). North Africa never did. There are Tunisian ruins were Roman wine presses are to be found in the middle of what is today desert. I don't see any magical invention changing that.