If not for the plague maybe the Empire could have taken the cost of expansion and became larger and stronger.
The parts of Italy that the empire held gave birth to the Papal State, Amalfi, Venice etc. Not always in the advantage of Constantinople but still decisive for the worlds history.
The roman past was more fresh in Italy then in other parts of the West, but there is no guarantee that Italy would have fared better in the long run.
A "what if" history when Justinian did not smash the goths would have still witness an unavoidable war with the growing power of the East, internal strife that had already begun, religious conflicts between the arian germans and the catholic majority, pressure from longobards and other barbarians and frankish interventions. All this problems were already there and the small effectives of romans used in Italy show a considerable goth weakness.
I don't believe in the idyllic (and panegyric) image of Ostrogoth Italy.