"Even with proper medication and diet, as many as two-thirds to three-quarters of people with Crohn's disease will require surgery at some point during their lives. While surgery does not cure Crohn's disease, it can conserve portions of your GI tract and return you to the best possible quality of life.

Surgery becomes necessary when medications can no longer control symptoms, or if you develop a fistula, fissure, or intestinal obstruction. Surgery often involves removal of the diseased segment of bowel (resection), the two ends of healthy bowel are then joined together (anastomosis). While these procedures may cause your symptoms to disappear for many years, Crohn’s frequently recurs later in life."

References: 

1. https://www.crohnscolitisfoundation.org/What-is-crohns-disease/treatment