Place chicken in a deep pot and cover with water; add sherry, onion, celery, salt, and curry powder. Bring liquid to a boil, cover pot, reduce heat to medium-low, and simmer until chicken is no longer pink near the bone, about 1 hour. An instant-read thermometer inserted into the thickest part of the thigh, near the bone should read 165 degrees F (74 degrees C).

Strain broth from chicken mixture into a bowl and transfer chicken to a work surface to cool until easily handled. Pull meat from the bones and cut into bite-size pieces. Discard bones, onion, and celery.

Heat butter in a skillet over medium-high heat; saute mushrooms until golden brown, about 10 minutes.

Bring reserved chicken broth and wild rice to a boil in a large saucepan. Reduce heat to medium-low, cover, and simmer until rice is tender, about 45 minutes. Drain excess liquid, fluff rice with a fork, and cook uncovered 5 minutes more.

Preheat oven to 350 degrees F (175 degrees C).

Combine chicken, rice, and about 1/2 of the mushrooms in a 4-quart casserole dish. Mix mushroom soup and sour cream together in a bowl and stir into chicken-rice mixture. Arrange remaining mushrooms in a circle on top of the casserole.

Bake in the preheated oven until bubbling, about 1 hour.