First of all, there's clearly no transition in place for Manu either. Jonathan Simmons?

Kyle Anderson?

Those two aren't solutions to a problem, they're part of the problem that warrants a solution. While I don't agree, I'm not surprised the Spurs overpaid Ginobili to come back for one more season. Otherwise, It would be death by a thousand cuts., literally.

A side note on George Hill, he was traded because the Spurs couldn't transition him into a pg. He wasn't a good fit next to Parker and he was blocked by Manu off the bench. It's funny how nearly everyone wanted George Hill gone before he was eventually traded but, now everyone wants him back.
Secondly, the Spurs did bring in C.J. McCollum and Jimmer Fredette as possible back up plans for Parker but they didn't pan out.
Thirdly, Patty Mills was listed as a pg for team Australia but make no mistake, Dellavedova ran the offense. Patty can't run an NBA offense for a playoff caliber team. If he could, he'd be the Spurs defacto back up plan for Parker. Also, had he been able to run the offense properly, he would have been the guy to take some of the added pressure off Ginobili during the regular season over the past two seasons. He couldn't. Patty provides instant offense off the bench when his shot is dropping but not much else.
Lastly, I have no sauces like 60% of Spurstalk but, I believe Duncan was semi forced into retirement with the addition of Pau Gasol. If Pau opted in to the final year of his deal in Chicago, I think Tim comes back for another year. But you know what they say....
Better to leave a year early than a year too late. That should actually be posted in the Spurs locker room, tbh.
