The international cycling union UCI, under new president Brian Cookson, is putting together an independent commission to investigate doping in the sport's past and says it will make contact with Armstrong about testifying.
Armstrong, who was stripped of his seven Tour de France titles and banned from competitive sport for life last year after admitting to using performance-enhancing drugs, has said he is willing to assist an inquiry.
However, even if he does that, Fahey does not believe it will lead to the 42-year-old Texan's case being re-opened or for it to have any impact on his ban.
"As far as I'm concerned it's done and dusted. Armstrong did what he did. We all know what that is. He did not cooperate, he did not defend the charges that USADA put out there last year and he was dealt with in a proper process," Fahey told a press conference.
"It would take something close to a miracle to change going forward."
Fahey also believes the UCI's planned independent commission is close to being finalised.
"I am confident that from what UCI have indicated, and their wish to get something going, that it will happen within weeks rather than within months," said the WADA chief, who is due to meet Cookson in Johannesburg this week.