This phase II trial studies the effect of capecitabine and temozolomide after surgery in treating patients with high-risk well-differentiated pancreatic neuroendocrine tumors. Chemotherapy drugs, such as capecitabine and temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving capecitabine and temozolomide after surgery could prevent or delay the return of cancer in patients with high-risk well-differentiated pancreatic neuroendocrine tumors.