By about 500, or 510, the Late Roman Army had vanished both physically and from primary sources, in the territory which once comprised the Western Roman Empire. It would make sense to see the army as disappearing due to the end of the Western Empire, but the reality is much more murky, because in more ways than once, the Late Roman Army didn't disappear at all.
SOURCES:
Warfare & Society in the Barbarian West, Guy Halsall
Barbarian Migrations & the Roman Empire: A counter-intuitive view, Guy Halsall
Barbarian Migrations & the Roman West, Halsall
The Late Roman Army, Southern & Dixon
