While agile methodologies are established in many software development processes, most of the research concentrates on the initial transition from traditional methods to agile practices. Relatively little attention is given to the challenge of staying agile in the development projects over the long term, especially when organizations face phases of declining agile maturity. This paper addresses that gap by presenting a comprehensive process lifecycle model that spans both the transformation phase and the subsequent periods when agile practices may deteriorate. The model integrates insights from a systematic literature review – focusing on phase models for both agile transformation and decline – with empirical data gathered from a six-year, long-running agile project. Through a focus group, concrete actions and best practices were identified that consistently helped the case project avert a loss of agility. Two cross-cutting results stand out: First, teams must actively reconnect with the core values of agility (transparency, iterative learning and customer focus) and translate them into day-to-day rituals. Second, short, well-timed external impulses (for example from agile coaches or specialized consultants) act as catalytic boundary spanners that expose blind spots and accelerate internal learning without undermining team autonomy. Taken together, the findings offer a practical guide for organizations striving to maintain agile performance and provide a robust foundation for future research into sustaining agile projects.