I am guessing if Fed can stay injury free then he will retire at the WTF next year. Fed has slowed down perceptibly. In the second half of this year, he has been beaten twice by Andy, beaten by Nole and twice by Delpo. I just can't see him winning many tournaments next year - maybe two or three, and definitely will get knocked out by the SF stage of all 4 GSs, by Nole, Andy, Delpo and Berdych.
His ego will get a massive hit and by the end of next year, others will take him out too making it impossible for him to continue if he wants to keep the GOAT title and respect