If the Viking invasions did not happen, then it would have been difficult to unify England. One only needs to look at Germany or Italy in the Medieval and early modern period to see that many states that exist today in Europe took a long time to develop as unified nation states. Kingdoms in early Medieval Europe, such as Charlemagne, were able to create larger monarchies or states; however, they soon became fragmented as children of the monarch or rivals would compete for power. On the other hand, areas most threatened by invasions became more likely to unite, as a greater outside threat helped to catalyze similar cultures to merge together to form a more powerful kingdom.
This was the case in England. We could, therefore, speculate that a lack of clear outside threat could have meant a longer continuity in the power struggles that affected England before the 8th century, specifically back and forth fighting between Anglo-Saxons and sometime Britons.