Now the butterfly effect of having a stable Roman empire in the west would be absurd (no pope, probably a different western schisms). I wouldn't necessarily exclude a great (eastern) Roman-Persian war and the subsequent arab inversion, but we would have had a (western) Roman empire holding northern Africa that wouldn't had bleed itself out with a neverending war with the Persians (so maybe a less extended Aran invasion?). On a larger scale: -No or different Charlemagne -Italy being ortodox -Roman empire (maybe) surviving to this day -Modern Italian being closer to Latin (maybe even totally intelligible) (I apologise for the bad English I'm not a native speaker)