Background: Sustained access to antiretroviral therapy (ART) is central to controlling HIV transmission and reducing AIDS-related morbidity and mortality. Recent funding uncertainties and policy shifts, however, threaten the continuity of ART provision in several high-burden settings. Methods: A deterministic compartmental model was developed to investigate the epidemiological consequences of disruptions in ART funding on HIV transmission and disease progression. The model incorporates treatment-induced viral suppression, progression to AIDS, and differential infectiousness between treated and untreated individuals. Analytical results establish the existence and stability of disease-free and endemic equilibria, and the control reproduction number Rc is derived to characterize threshold dynamics. Sensitivity analysis using Latin Hypercube Sampling and Partial Rank Correlation Coefficients identifies key parameters influencing Rc. Results: Numerical simulations indicate that reductions in ART coverage, even by 50%, can substantially increase viral rebound, elevate HIV incidence, accelerate progression to AIDS, and raise HIV-related mortality. Sensitivity analysis highlights ART coverage, early treatment initiation, and viral suppression rates as the most salient factors driving epidemic outcomes. Temporary or sustained interruptions in ART funding can therefore reverse decades of treatment progress and trigger epidemic resurgence. Conclusion: The findings provide quantitative evidence to inform policy decisions, underscoring the critical importance of maintaining uninterrupted ART programs. Targeted interventions that sustain treatment coverage and enhance viral suppression are essential for long-term HIV control.