I know everyone is asking that question and there is no other way to know than to see him play but we do know he'll never be the same again. I personally, see him losing much of the athleticism (particularly the agility) that made him such a unique talent at his height but I don't think it'll necessarily be the end-all/be-all of his impact on a game. He's still a 7ft giant that is a marksmen from deep, which offers it's own utility in this league.
The true Greats have all had to re-invent their games at some point in their career; this will be Durant's opportunity to do the same. Personally, I see him developing into a 5-man in the vein of what Chris Bosh was for the Heat. Durant was featured in lineups with the Warriors, where he was the rim protector and proved to be effective rotating to the weakside, so he should be serviceable on that end. I'm iffy about how his rebounding ability projects moving forward but he's managed to get about 8 a game primarily as a perimeter player, which is encouraging. Whatever the case, we'll have to get him a grittier 4-man to offset the fact that Durant will always be a little light in the shorts. With that being said, is Durant as a future 5 worth the investment? Or is his appeal tarnished if that is the case?