Although there is no precedent for returning captive elephants such as Billy to the wild, there is an alternative: Sanctuary. There are currently two Sanctuaries in the United States devoted to providing a life of dignity and autonomy within a safe, appropriate habitat for elephants imprisoned and traumatized by the entertainment industry. The Elephant Sanctuary in Hohenwald, Tennessee, provides a permanent home for captive elephants on more than 2,700 acres (www.elephants.com). The Performing Animal Welfare Society operates a 2,300 acre sanctuary in San Andreas, California for elephants and other captive wildlife, and is a "dedicated endeavor to provide the best quality of life for victims of captivity." (www.pawsweb.org). While Sanctuary can never replace life in the wild, and the concept in no way justifies or endorses captivity, it provides a space where "individual elephants may recover a more naturalistic life in captivity to the extent they are capable of doing so given their history." (Sanctuary for Elephants - Overall Principles, www.elephantvoices.org).
For further discussion of elephant trauma recovery and the concept of Sanctuary (as opposed to zoos), please see this article in Psychology Today: