Seismic risk in Italy is significant due to its high population density, the presence of large historic centres, the existence of diffused ancient hamlets in inner areas, and a built heritage consisting largely of old buildings. It is imperative to adopt strategic approaches focused on reuse, restoration, and adaptation to preserve historical and cultural values while promoting sustainability by reducing the impact of new urbanization. This paper proposes an empirical-performance method for an expedited assessment of the seismic vulnerability of damaged buildings. A set of 27 abandoned buildings located in the historical centre of Conza della Campania (Italy) and severely damaged by the 1980 Irpinia earthquake, is used as a case study. The study begins with a typological classification of the buildings, from which capacity curves are derived using a mechanical approach. Based on these curves, a second set of residual capacity curves is derived. By acting on the parameters of yielding acceleration and yielding displacement, these new curves enable consideration of the reduction in stiffness and strength linked to the degree of damage observed. Then, two different scenarios are considered, evaluating the impacts of a future earthquake first according to the residual curves and then following seismic adaptation measures. The demolition, transportation and reconstruction costs of the first scenario are compared to the retrofitting costs of the second scenario. The results and the comparative approach proposed provide valuable insights to implement reuse and rehabilitation strategies for the built environment, promoting sustainable regeneration of inner areas.