The analysis presented in this paper deals with two main issues: the one of debt sustainability, meant in the particular acceptation proposed in this article, and the one of the effects of debt decumulation for the various territorial communities, in particular for the weak areas of Italy (Mezzogiorno). The sustainability refers to the effects of the governmental financial situation on the growth rate of available resources for the purposes of consumption and investment. The proposed exercise aims at showing some possible outcomes of the economic and financial crisis that is taking place. Actually, the hypotheses proposed do not lead to a prevision, but to a prediction, that is a sort of prophecy deduced from a very limited set of data. Four hypotheses, concerning the constraints of various kinds regulating the variation over time of the debt amount, are proposed: firstly, the zero debt (or constant debt) hypothesis; secondly, the case of the invariance of GDP-debt ratio; thirdly, the hypothesis of a ceiling on public debt and, lastly, the case of a programmed path of public debt reduction, such as the fiscal compact[...]