Following up on this post, David Lat of Above the Law has obtained this statement from the Court:

Justice Kennedy is in the process of hiring clerks for 2017. The Justice didn’t go to Salzburg this past summer because it conflicted with some plans with his family, but he is scheduled to return to teach there in 2017. The reunion is scheduled for the end of this Term because the Justice’s law clerks wanted to hold it during the Justice’s 80th year to mark his birthday.

David adds:

 This statement, which presumably reflects input from Justice Kennedy, strikes me as a persuasive and well-founded rebuttal to the rumors. If AMK were planning to retire next year, the easiest thing would have been for the Court to offer a simple “no comment.”