Supposing that Byzantium was not destroyed in 194 AD, and in the face of that strong citadel on the Sea of Marmara the East Germanic people decide to to stay on in the northeastern coasts of the Black Sea. The Bastarnae, Goths, Gepids, Heruli, Lemovii, and Scrii (and maybe Rugii and Vandals too) unite with the Alans under a strong kingship with a stable line of succession. Their settlements around Crimea grow up into a comparatively centralized kingdom that extends east to the Ural River.
The Gothic-Alan Kingdom keeps the Huns disorganized and fourth century comes on with a stable border kingdom to the north of the Eastern Roman Empire.
What do you think happens?