I then looked at the following website that is dedicated to Endangered Languages
It is described as "the world through 3054 lenses: an online collaborative effort to protect global linguistic diversity". I noticed that Wiradjuri is listed as "critically endangered, with 3 native speakers worldwide in 1981." They provide a document defining endangerment and extinction.
I am not sure that Wiradjuri is extinct or critically endangered:
In 2009 I learned Wiradjuri for a year and received a Certificate 1 in Wiradjuri from the NSW Technical and Further Education Commission of Australia. During this course I met and learned from Wiradjuri speakers.
Last week, I asked the authors of the Longitudinal Study of Indigenous Children if they knew of children on their project that spoke Wiradjuri. They said that there were.
UPDATE 20th August 2012
I look forward to working further to find out more about the actual status of Wiradjuri