FYI bumping without content is considered rude round these parts.Bump !
Honestly, having the Sassanids invade might lead to Palmyra's survival, since the Persian pressure means they won't go after other Roman provinces.I think Palmyra would be too tempting for the Persians...
You mean a germanic raid on the Port town of byzantion?Perhaps have the Gallic empire last longer and the western empire collapse into various successor empires and warlords fighting for Western Europe, combine that with Germanic invasions of Greece and Constantinople, combine that with Persian distraction or weakness and you have a far longer lasting Palmyrene empire. Though as stated it would require a lot of luck and things going in ways it could not control.
I mean the Germanic tribes raid and invade Greece-maybe not Byzantium but at least devastate and or conquer what would become the heart of the eastern Roman Empire.You mean a germanic raid on the Port town of byzantion?