He has been talking about it on bubble for a while and nobody knew if he meant it, so it's still not sure whether he will leave or not. But there is a high probability.
It really doesn't change much, he can't dance or won't join tours anymore, always saying he's a burden to SJ due to his injury. I think it will be a very friendly leave, even Leeteuk said to members if it gets too hard, they can leave this time.
So let's just be prepared emotionally in case.
edit: actually he said his contract is ending, not sure whether it's a SM or SJ contract, we'll see
edit2: Super Junior members recorded Knowing brothers yesterday suddenly as a full group, might get special I imagine