This study investigates the mechanical response of rockfall-induced fragmentation by implementing a novel numerical breakage model within a discrete-element framework. The model evaluates the size distribution and breakage probability of rock blocks upon impact, considering key variables such as impact height and initial rock size. The system consists of a rock buffer layer and a freely falling rock block, with irregular geometries incorporated for greater computational realism. Results highlight the strong influence of impact height and rock size ratio on fragmentation, increasing the breakage probability as energy dissipates through the medium. Notably, rock fracture does not always occur instantaneously upon impact but may be delayed by milliseconds as stress propagates through the granular bed. A simple probability model is proposed to estimate the survival rate of rock blocks based on impact height and rock size, demonstrating strong agreement with reported rockfall cases in caving mines. This approach enables back-analysis of rockfall conditions prior to secondary fragmentation, aiding in the understanding of fragment behaviour within the mineral column before extraction. Additionally, the findings contribute to geomechanical risk mitigation by offering insights into rock mass dynamics and energy dissipation mechanisms during impact.