I think when KD is back, he will still be fit but the bounce and his agility will be minimized since his injury is very serious that he will stop playing for one year or more if it gets aggravated. Now, the future of the GSW rely on how well they manage their line up without KD to be back to the finals next season.
Most of the superstars that came back from injury, they weren't the person that we knew.
Their performance changes, their endurance and everything. It's true that his agility and other attributes will be changed to minimize because he has to protect himself. The team is no longer in the hands of KD but to the team as a whole.