Right now I think the depth chart looks like:
Parker
Ginobili
Bowen
Duncan
Oberto
Backup points: Vaughn, Hill (if you want to keep going down the line ... Ginobili, Mason)
Backup wings: Mason, Udoka
Backup bigs: Bonner, Ian
The Spurs lack of depth is scary.
Of course, it's July so who knows by October. If Thomas doesn't come back, the lack of bigs is pretty daunting. And I'm not sold that Gist or Tolliver will be on the Spurs. Plus I wouldn't be surprised if players like Udoka, Bonner or even Ian get dealt in the right deal.