China’s nationwide Spartina alterniflora eradication program across 18,000 km of coastline aims to restore native biodiversity, but removing these carbon-rich invasive stands is estimated to release 21.4 Mt CO2. This challenge is compounded by accelerating sea level rise, which threatens the native replacements meant to restore blue carbon functions, and current restoration approaches lack systematic strategies to address both pressures. We coupled species distribution modeling with the Sea Level Affecting Marshes Model (SLAMM) to project the performance of two posteradication restoration strategies─Environmental Suitability (ES, prioritizing habitat preferences) and Optimized Carbon Stock (CS, prioritizing high-carbon species)─under SSP1–2.6 and SSP5–8.5 through 2100, and quantified the minimum inland migration area required to sustain a target carbon stock (2.16 Tg C). Across projections for 2060 and 2100, tidal marshes outside seawalls are projected to lose 23–50% of their area, with carbon stocks declining 12–51% relative to 2021 levels. The CS strategy maintained 6–16% higher carbon stocks than ES. Mainting the target carbon stock required 31–157 km2 of inland migration space, with CS’s advantage over ES in reducing migration requirements narrowing from 37% under SSP1-2.6 (2060) to 4% under SSP5-8.5 (2100). These results show that management strategies lose effectiveness under extreme climate conditions, underscoring the value of early intervention under low-emission scenarios, and offer practical migration-space targets for coastal planning wherever invasive species control intersects with accelerating environmental change.