Sauté onion in drippings in a large Dutch oven. Add chicken, and brown on all sides. Add water, tomatoes, sherry, and Worcestershire sauce. Bring to a boil; cover and simmer 30 minutes. Remove chicken from liquid, and cool. Bone chicken, and cut meat into 2-inch pieces. Return chicken to liquid. Add vegetables. Simmer, uncovered, 1 hour, stirring occasionally.