They were a real shooting star, weren’t they? The Avars went from being a random Germanic tribe to dominating Gaul and Hispania, only to completely fall apart after Armorica.
I hate to be 'that guy', but they weren't technically Germanic. They were an Altaic group that overran Europe after the Hunnic collapse, and eventually adopted the Germanic loan words and customs from their subjects. But like their Hunnic predecessors, and like the steppe hordes that would follow them (Magyars, Alans, Neohephalites, etc) they basically disappeared once their leadership collapsed. I do have to wonder what would have happened if they'd won in Armorica though. An Altaic Manichaean elite ruling over a Nicean Romano-Gallic population would have been interesting to say the least.