Oseltamivir resistance in influenza virus, primarily driven by the H275Y substitution in neuraminidase, emerged as a critical public health concern during the 2007-2009 pandemic period. This study presents a Wright-Fisher population genetics model integrating antiviral drug pressure, viral mutation rates, and population-level transmission dynamics to predict antiviral resistance emergence and prevalence. We parameterize the model using empirical data from the 2007-2009 pandemic period, including oseltamivir prescribing patterns (peak ~100M doses/year in US), neuraminidase H275Y mutation frequency (0% baseline, peak ~30% in 2008-2009), and viral fitness penalties (estimated 20-50% transmission cost for resistant mutants in untreated hosts). Monte Carlo simulations (10,000 replicates) over 5-year horizons demonstrate that resistance prevalence depends critically on the threshold of untreated infected individuals. When treatment reaches 40-60% of symptomatic cases, resistant strains remain at <5% frequency despite continued drug pressure. Resistance emerges explosively when treatment coverage drops below 30%, with variants reaching 30-40% prevalence within 18-24 months. The model identifies a tipping point at approximately 25-35% treatment coverage where stochastic fluctuations determine whether resistance sweeps through the population. We validate predictions against observed 2007-2009 epidemiological data showing H275Y prevalence correlated with oseltamivir use patterns across regions. Sensitivity analyses show resistance emergence is most sensitive to mutation rate (±50% change alters predictions by 8-12%), fitness cost of resistance (±30% changes alter timeline by 6-10 months), and treatment rates (10% change in coverage shifts tipping point significantly). This framework enables public health forecasting of antiviral resistance emergence to guide antiviraldrug stewardship policies and pandemic preparedness planning.