I have been so happy to see Rozier's development through the year. He is so much better with the ball, and is a competent point guard. He has a major clutch gene and can hit timely buckets, he works hard on def, is a great rebounder for his size. His shooting has improved as his minutes have been increased.
I guess the question is how much more will Rozier develop, and does he have the opportunity to develop playing behind Kyrie. I think the answer is no. I also think he might command big (ie more than we want to pay a backup point/combo guard) money in free agency depending on how well he plays next year. So I think unless something bad happens to Kyrie, DA will eventually trade Rozier.
I hope that doesn't happen next year but it might. It would be great to have Terry as a backup for one more year in a title push for 2018-2019.
But does he make Kyrie expendable, no way. It isn't even a sure thing that Terry will develop beyond how well he is playing right now, much less take 2-3 more leaps up to the point where Kyrie is at.