Conventional biorefining of lignocellulosic biomass, such as corn stover (CS), is hampered by poor carbon efficiency, as nearly half of the substrate carbon is lost as CO2 during ethanol fermentation. This study presents a holistically integrated cascade process designed to capture and valorize all major carbon streams. The system synergistically couples three stages: (1) high-productivity ethanol fermentation (1.68 g/L/h) using the engineered yeast Saccharomyces cerevisiae CE10; (2) anaerobic digestion of the resulting stillage, which efficiently converted residual organics into methane (171 L/kg COD) with ca. 80% COD removal; and (3) cultivation of the cyanobacterium Desertifilum tharense BERC03 using the nutrient-rich digestate and captured fermentation CO2. This integrated approach boosted the carbon utilization from a baseline of 48% to 62%. A comprehensive techno-economic analysis of an industrial-scale (2000 t/d) facility projected a Minimum Ethanol Selling Price (MESP) of $2.44 per gallon, a value approaching current market competitiveness. The analysis identified the feedstock (30%) and cellulase (17%) as the primary cost drivers. These findings demonstrate a validated biorefinery model that significantly enhances carbon recovery and outlines a viable pathway for the coproduction of multiple biofuels from lignocellulosic resources.