Kelvin De Bruyne without doubt is a very important member of the Manchester City team and he really proved his worth when he featured for the club for the first time in over four months after picking up injury in August last year. His performance in that game was simply breathtaking as he came from the bench to score a goal and provide an assist for another to help Manchester City come from behind to take all three points against Newcastle United during the weekend.
Kevin and Manchester City are trying to enjoy their last happy seasons because the career of Kevin is counting down. He is returning impressively from his injury and if he continues, he will help Manchester City a lot in coming months when both Premier League and Champions League will come to most important months in this season.
However we must be realistic about Kevin as he is older and his body will become more sensitive with injury. With abundant money in Manchester City for player transfer, they will not have need to keep Kevin in their club and soon they will say goodbye with Kevin. Winning one more Premier League and one more Champions League will be a perfect goodbye from Kevin.
He is not "that" old yet, dude is 32 years old, Modric is still playing fairly decently at Madrid at age 38 right now, I think if Modric can do that, then I could guess that there is no reason why Kevin can't do that, it would mean another six years of him, that is a lot of time in football terms, teams do change players a lot more often than that.
I understand that it may feel a little weird at first, but it does look like a good thing in the end. I believe that the best thing to do in this case would be just let him be and let him show you when it is done. If he starts to play badly, then you can cut him, but until he does, there is no need to think about the future, he is still there to give all he has and that is a good talent right now.