In some ways Justinian actually hastened the destruction of some of the "Roman" elements of what was left of the Roman Empire. The Ostrogothic Kingdom in Italy, though ruled by Germanic Kings, was heavily influenced by Roman culture and life for the people in Italy under the Ostrogoths was similar to how it was under the Roman Empire. Justinian's war with the Ostrogoths was long, drawn-out and extremely destructive to Italy. His use of the Lombards as allies/mercenaries also led to the eventual Lombard conquest of Italy, and the Lombards were nowhere near as Latinized as the Ostrogoths.

The situation in Africa was a bit different. Justinian's reconquest of the Vandal Kingdom was actually very quick and not all that destructive, and it was reincorporated into the Empire and was a wealthy and important city. This is reflected in the way Carthage was the stopping point for the Arab invasions later on--the Emperor Constans II tried to re-center the Empire around the former lands of the Vandal Kingdom. He made Syracuse his base of operations rather than Constantinople (I don't think it was ever an "official" capital, but he spent a lot of his reign there) and fortified Sicily and Carthage so that the Empire had a stronghold bisecting the Mediterranean. It was pretty successful and delayed Muslim progress into Africa for about 50 years. So while Justinian's reconquest of Italy was pretty much a failure and a huge waste of resources, Africa was successfully reintegrated into the Empire and served an important role during the wars with the early Caliphate.