This study aimed to reconceptualize university student dropout as a process-oriented phenomenon in which accumulated academic experiences and enrollment status changes unfold sequentially, rather than as a singular event. To this end, 9-year integrated administrative data of undergraduate students at University A were utilized to explore structural pathways from academic achievement to dropout, mediated by academic probation (AP) and leave of absence (LOA), from a time-series perspective. In particular, by applying path analysis based on structural equation modeling and bootstrapping procedures, the study empirically identified a serial mediation structure in which the two mediators operate sequentially. The results indicated that the sequential serial mediation pathways—from low academic achievement through AP and LOA to dropout—were significant for all variables; conversely, the direct effect of AP on dropout was found to be non-significant. This implies that AP functions as a transitional mechanism that indirectly influences dropout by inducing the behavioral choice of taking a leave of absence, rather than causing departure on its own. These findings provide empirical evidence that university student dropout is a dynamic process of accumulated academic crises and enrollment experiences. Furthermore, they offer educational implications regarding the necessity of establishing a proactive enrollment management system that not only intervenes at the AP stage but also manages the transition to LOA and supports student return to prevent dropout.