You shouldn't be torn at all. The Spurs are developing players (like Simmons, who plays at his position, SG and exactly 0.4 mins less per game than Manu this season). Manu just has a relatively high usage (albeit in low minutes), simply because he's still a net positive out there. Even if Manu retires, I don't think it's automatic that, say, Murray takes his minutes. I think Murray's situation is more closely tied to what PATFO does over the summer with Patty.
What some of you need to realize is that the Spurs are not really rebuilding. Time for the younger guys will come here and there, and they need to show they've earned it. Take last season for example. The Spurs could've given more run to Kyle or Simmons, but PATFO brought in 33 years old Kevin Martin mid-season instead. If you want Pop to play the kids more, they either need to be extremely good, or wait until the team is tanking, tbh.
I've no idea what Manu is going to do, tbh, he probably doesn't know either. But it wouldn't be surprising at all if PATFO goes out there and gets another vet if he retires. They get to look at the kids plenty during the season and practice, they know what they have, what they can trot out there and not.