I think that Frankish culture combined with the Romano-Celtic one to create modern France. I'm not sure that the Franks disappeared; after all, the country which they occupied is today named after them - France- as is the people - the French. The same can't be said about the Gauls, whose language and culture became completely extinct in the years following the fall of the Western Roman Empire. Nobody who now lives in the territory of what used to be ancient Gaul call themselves Gauls, Celts, Belgae or Aquitani. In that respect the Franks were much more successful than the natives, although the Romans ultimately triumphed as the French language is derived from Latin. I suppose the biggest losers in this sense are the Gauls, who lost their language, culture, religion and identity. At least the Romans influenced the future language of France, and the Franks its culture and identity.