TBH, these young core of the Spurs now are nowhere near to the big 3 of the spurs before (Duncan, Parker, and Ginóbili). so I don't expect spurs will be successful if they will not get another star players that have already prove himself from a team he is playing with now.
I think we will never see this kind of line up of the spurs anymore, and coach pop time with the Basketball will be over soon, so we can't expect that the one who inherit the coaching job will be as good as him. I heard Timmy has a good chance of getting that spot, anyway, that's just a rumor, but I'll be very glad to see him as the coach of the spurs and let's see if he can be a great coach like a player he was.
https://www.expressnews.com/sports/spurs/article/Tim-Duncan-s-future-a-hot-topic-after-San-15105988.php