Adaptation and sustainability are two key challenges leading the development of software-systems nowadays. Adaptation denotes the capacity of a system to address variations and uncertainties at runtime in order to continue providing its functionalities with certain quality levels, notwithstanding change. But how can adaptation and its intent be expressed at design time so that to analyze its possible impact at runtime over a long period of time? To answer this question we look at adaptation from the sustainability point of view. Sustainability denotes the capacity of a system to both endure and preserve its function over time. We propose an approach which uses decision maps to make sustainability-driven decisions for adaptation in a systematic way. The proposed approach is illustrated through two self-adaptive exemplars as illustrative cases.