<p>Hybrid integration of Low Earth Orbit (LEO) satellite systems with terrestrial networks is a critical facilitator for beyond-5G connectivity, especially in situations where terrestrial coverage is constrained by cost or feasibility. At Ka-band frequencies, link performance is extremely susceptible to propagation impairments, including rain attenuation and atmospheric absorption, as well as terrestrial interference resulting from coexistence with ground-based networks. This study offers a simulation-driven, system-level analysis of hybrid LEO-terrestrial downlink performance. A Monte Carlo framework integrates established propagation models, free-space path loss, ITU-R P.676 atmospheric absorption, ITU-R P.838 rain attenuation, and Rician small-scale fading with a distance-dependent, spatially distributed terrestrial interference formulation. The emphasis is on identifying performance regimes and reliability limitations resulting from the cumulative effects of environmental and interference factors, rather than suggesting new channel models. The study measures received power, SNR, SINR, outage probability, bit error rate, and spectral efficiency at different satellite altitudes, carrier frequencies, rainfall intensities, and levels of interference. The results show that the satellite signal weakens with increasing slant distance, causing a transition from noise-limited to interference-limited operation, and demonstrate how rain attenuation degrades Ka-band link reliability. This work further illustrates that sustaining link reliability under adverse conditions requires adaptive adjustment of performance thresholds. The simulated SNR and capacity values for clear-sky conditions are verified against published Ka-band link budget benchmarks and ITU technical data. The results offer system-level perspectives for the design and planning of hybrid satellite-terrestrial communication systems.</p>