First you have to ask yourself what time period and in what extent the "Dark Ages" took place. I don't subscribe to the belief that it was quite as bad as most people think. For instance, you do have a few renaissance's that take place, probably most notably the Carolingian Renaissance. Yes, the Western portion of the Roman Empire completely collapsed and engineering and economies more or less collapsed as well. But at the same time you're ignoring the Byzantine Empire which survived almost the entirety of the time frame referred to as the Dark Ages. Meanwhile even further east you have the Islamic Golden Age occurring during which huge strides where made in the sciences, namely medicine.

Sorry for the history lesson, but while one area might be experiencing a "Dark Age" due to the collapse of an Empire, many other areas are flourishing. I think that in the Early Middle Ages especially, the general disarray (hah) that took place following the collapse of the Western Roman Empire prevented advances being made elsewhere from coming in from elsewhere. In today's world I can't see such a thing happening, at least not easily. Everything seems to be far more interconnected a globalized, and it would take at the least a regional collapse to even think of such a thing.