Well... Kawhi opted out too. He can get paid WAY more for doing this. I think Kawhi is staying in TOR.
No, technically they could apply but the NBA isn't going to grant them one for signing an injured player. Besides Durant is probably going to miss the year but it's possible he could still be back so a doctor isn't going to approve it. As discussed before the disabled player exception isn't enough to really make a difference in this situation anyway. It would be about $9 million.
I don't get it. I would not sign someone who just ruptured his Achilles to max contract at this point. I have never seen a player return from that injury without significant degradation of their game.