So it seems that
G.Washington_Fuckyeah's
thread on this topic has become buried in spam about whether or not getting rid of the Plague in the first place is doable, which is a shame, because the potential butterflies seem quite interesting. Accordingly I hope Mr.
Washington won't mind if I start this new thread to focus on the outcome of the POD, rather than the POD itself.
Can the Roman Empire defend the conquests of Justinian (mainly Italy) against the Lombards if there is no plague of Justinian/if the plague mostly hits Persian territory and barbarian populations (Arabs, Visigoths, Lombards)?
(If anybody wants to contest the POD itself, and tell us that not having the plague is ASB, could they please do it over
here.)
As for the question posed, I've heard a theory that the reason the Byzantine Empire was hit worst by the plague was that the surrounding regions were generally either too dry for the plague to flourish (Persia, Arabia) or too cold (Northern Europe). If so, it would probably be more plausible to butterfly away the plague entirely than to make it hit the Empire's enemies worse.
Interestingly enough, Justinian cancelled the pay of the limitanei frontier troops in 545, just a couple of years after the Plague struck. I wonder if this might have been due to the economic damage caused by the disease. In previous conflicts during the 4th and 5th centuries the limitanei had shown their worth, garrisoning important cities even after the Roman field armies had been badly mauled and so helping to avoid defeat turning into disaster. If the Empire was able to keep them around, it would almost certainly be in a better position both to keep hold of its new conquests, and to resist the Slavic/Persian/Arab invasions of the 6th and 7th centuries.