There are no many threads about an eventual no-Justinian scenario, and the few I checked are mostly focused on the fate of the Byzantine Empire (war with Sassanians, Arabs etc.).
But what could have meant to the West a non-expanding Byzantine Empire which had stuck to the East and eventually stopped the expansion of Arabs/Turks/Iranians whoever to the West during all/most of the Middle Ages?
Many questions here:
- Would the Ostrogothic and Vandal Kingdoms succeed and prosper, or they would have fallen anyway?
- Would the Lombards migrate into a still Ostrogothic Italy anyway?
- Would the Franks expand as successfully as IOTL?
- Would the Visigoths endure and challenge the Frankish hegemony in the West? Maybe also the Ostrogoths?
- Would any restored Western Roman Empire/HRE be formed at all?
- Would Rome decay under continued Ostrogothic/Lombard dominion? Would the Papacy survive such situation or might be the Western Church would evolve into a multihead hierarchy?