A 68-year-old Indian man with a 10-year history of smoking presents with gradual painless central vision loss over the past 18 months. Fundus examination reveals large drusen (>125 μm), retinal pigment epithelium (RPE) atrophy with a sharply demarcated pale patch, and visible choroidal vessels through the atrophic zone. The foveal center marked **D** in the diagram remains relatively spared at present. Which of the following best describes the natural history and prognosis of this patient's condition?