Apologies, this is ENTIRELY inspired by The Last Roman DLC for Attila : Total War, but I have to admit, I was intrigued.
What if, after the capture of Carthage, Belisarius declares independence, or at the very least refuses to hand over control to Justinian (essentially the same).
How could this 'Kingdom of Rome'/'Kingdom of Africa' have completed the task of conquering/uniting the former territories of the Western Roman Empire, and have Belisarius declare himself the Western Roman Emperor.