To ensure systems sustainability in delivering services, software maintenance (SM) is a necessary condition to solve emerging errors and satisfy new requirements during operation. This maintenance involves a great variety of interdependent elements and processes as well as requires competent and motivated staff.This research aims at developing a model capable of explicitly explaining the complexity of causal feedback-relationships between elements and processes of SM and information systems (IS) staff management related factors. A preliminary causal loop diagram of system dynamics method was developed from literature. A successful e-government system of a Ministry in Indonesia was selected as the case. IS staff and managers of the selected case were deeply interviewed using prepared questionnaires developed based on the preliminary model. Data collected is used to validate and refine the preliminary model. The resulting empirical causal loop model explicitly describes how various factors, which might not be close in space and time, through chains of causal relationships, influence software availability level over time, hence IS sustainability, and how this level influences back those factors. Therefore, the model helps management with further insight about aligning an important domain of information technology with people to attain system sustainability.