Could you elaborate on your question a bit?

If you're asking "At what point did the Western Roman Empire cease to exist," there's several commonly offered dates, including the popular ones of 476 (resignation of the last officially recognized emperor Romulus Augustulus) and 480 (death of Julius Nepos, deposed Western Roman Emperor in exile), or the less popular date of 486 (fall of Soissons, a Roman Imperial rump state in northern Gaul that was conquered by the Franks in 486).

The problem is that the lifestyle of especially your average Italian wasn't vastly different in 460 than it was in 520, under a Visigothic kingdom that maintained a Roman Senate, law code, coinage, and more. The actual structure of Roman life was not dead by 476 or 486, and it took time for the post-Imperial world in the West to emerge as its own thing (and North Africa and Italy would fall back under Roman rule in the 530s, further complicating this process).

EDIT: Peter Heather's books would interest you, both The Fall Of The Roman Empire and The Restoration of Rome especially.