No way KG is retiring. He's playing until his legs fall off. Also even if people still want to say his skills have declined a bit, he is still an above average offensive player with a lethal mid range game, he's a fantastic rebounder, and he is a dominant defender.
If he walks away he would be leaving the game with still A LOT of value to give. And of all the NBA players KG seems like he would be the last to walk away when he is still giving a ton.