Using data from an obsolescent dialect situation in northern France, this paper questions the view that dedialectalization is a process of level-by-level attrition which leaves a linguistic residue in Regional French (the ‘Structured Obsolescence Hypothesis’). Comparison of dialect index scores for a number of variables reveals significant variation in rates of attrition within levels, with some phonological and morphological variants showing greater vitality than others, but no consistent relationship between levels as the model would predict. An alternative model is proposed, based on the relative learnability of different variants, and it is further argued that rejection of the Structured Obsolescence Hypothesis calls some other assumptions about Regional French into question, notably the view that it can be considered an intermediate variety between dialect and standard, and that it is necessarily ephemeral in nature.