I doubt Green opts in tbh. He fired his agent and his new agent only gets paid when he has a new deal that he helped negotiate. Green probably takes a 3 or 4 year deal, for less than $10 million per year. Thing is, the teams that will have cap space are generally bad and probably aren't going to want him because of his age and they don't need a veteran for more than the minimum the playoff teams that would want him won't have the cap space- or even the full MLE (Cleveland, Washington, OKC, GSW, Portland, etc.)
I could see him re-signing for 3 years, $27 million or 4 years, $36 million-that's more than what the MLE would be, even though he probably wouldn't even get that on the open market.
As what he said about Kawhi, I don't buy it. Him and Kawhi seem close and he's probably doing him a solid because Kawhi is getting killed for peacing-out on the Spurs this season. That doesn't mean that he won't be back but if the Spurs decide that he isn't worth the supermax then they'll trade him-hopefully they'll come to a conclusion by the draft though.