The conquest is narrated through both the Coptic chronicle tradition and later Arabic accounts, which characterize the fall of Byzantine Egypt differently, and neither the individual sieges of the fortress of Babylon and of Alexandria nor the campaign as a whole has been given a casualty figure by modern historians.
What would resolve this A source critical study comparing the Coptic and Arabic accounts of the conquest's losses, combined with a historian's estimate for the sieges of Babylon and Alexandria.
OpenEarly Islamic history, Coptic history, source criticism.Hugh Kennedy, The Great Arab Conquests: How the Spread of Islam Changed the World We Live In