Tommy Westphall was the autistic son of Dr. Donald Westphall and his deceased wife. The demands of caring for Tommy, combined with the frustrations of a changing St. Eligius, led Donald to leave the hospital in season 6, after which he relocated with Tommy to a quiet life in New Hampshire (as depicted in season 6’s “Their Town”).
https://en.wikipedia.org/wiki/List_of_St._Elsewhere_characters