Count Roger did not liberate Malta. Count Roger pillaged the island and went off with a few slaves, possibly Christian. Apparently Arabo-Berber influence lasted till as late as the 14th century where names such as Mohammed still appear among the local militia. But before I get carried away by my interest in Maltese history I would like to refer you to historians like Brincat, Wettinger and Luttrel who wrote extensively about the Medieval period. Unfortunately much still needs to revealed about this era.
More sources have to researched, especially new ones.
Ours have always relied nearly exclusively on the European ones which intrinsically tend to be biased because they would want to glorify their impact on history. So by searching other nevertheless not unbiased sources we can perhaps strike a balance. Brincat has published a very compelling pamphlet about a new version of medieval Maltese history. The book is called Al Himyari's Account. If his theory is proved right we may well rewrite our Medieval history afresh.