First of all, I hope I don't get bashed for necroing this thread, even more considering this is my first post, but I'm a longtime lurker here.
Currently I'm working on a ATL with the same old-fashioned idea of keeping the Western empire alive as a political entity after the 5th century, even if just on the Italian peninsula. Your TL was the only one I found so far that deals with a PoD in the late 4th/early 5th century, the exact period I wanted to start with.
So, it certainly serves as inspiration

, specially considering your approach, dealing with multiple POV from the "barbarian" peoples and Roman alike, is very ambitious. For now I won't even try replicating this formula, prefering to focus on the western Romans. Perhaps after I mature the scenario I might feel more comfortable with exploring different POVs.
Anyways, I find this period the most interesting of Late Antiquity, and, in my opinion, the latest period in which the empire could prevent its ultimate destruction (I believe after F. Aetius and Majorian, its ruin was inevitable). Also, I wanted to work with a Christian empire instead of a polytheistic one, so it had to be a PoD after Constantine's conversion.
I wrote a short story explaining the PoD. So far, I've killed off Honorius and Alaric early on, in 402 A.D., the first Visigothic invasion of Italy, and have Stilicho elevated to the purple, facing opposition from the Eastern empire. In an effort to atribute legitimacy to his unexpected ascension, he allies with the remnants of Theodosian dynasty in Spain, and is formally adopted by them. Now styling himself Theodosius II, he tries to bury his barbarian heritage and facing large scale invasions on the Rhine and the Danube, as happened IOTL. For now, the sketch I prepared for the 5th century determines that his dynasty won't be long-lived, but it will delay the collapse of the State.
Now, the migrations are "tweaked" to be, while much destructive, on the long-run less world-shattering to the Western Empire. For a couple centuries, Gaul, Britain and Illyricum are seized by foreign rulers, but I'll be sure of keeping them out of Spain, Africa and Italy. Eventually, the barbariam kingdoms might evolve into more formidable, but less hostile neighbors, while some provinces will be reconquered. Certainly it will have a Justinian inspired reconquest of former western provinces.
Great work here, pal, I'll try reading it as soon as I can.