The Spurs have employed a nine-man rotation since Bonner's injury. At this point in the season, I can see them going back to a ten-man rotation, but not eleven. So who falls out of the rotation?
At the time of Finley's injury he had been reduced from starting SG to backup SF and was playing around 12mpg. His injury moved Manu into the backup SF role and opened minutes at SG for Mason and Hill.
Bonner was averaging around 20mpg as the 3rd or 4th big in the rotation. His minutes have largely been filled by an increase in minutes for Blair and a marked increase in smallball from the early part of the season. The increase in smallball further increased Mason's minutes as he played SF in smallball sets in addition to his minutes at SG.
So Mason has the most to lose when Bonner and Finley are ready to play. Bonner will, IMO, almost certainly get back a spot in the rotation, perhaps at the 15mpg level rather than at 20mpg. Most of Bonner's minutes will come from a return to early season smallball levels. This will negatively impact Mason's minutes.
The impact of Finley's return is more difficult to predict. He could go back to a role as backup SF playing about 12mpg. At least 4 of those minutes could come from reducing Manu from the 29mpg he has averaged in January back down to about 25mpg. The other 8 minutes would hit Mason the hardest.
The other possible option is for Finley to be reduced to Hairston's role plus a few minutes as designated shooter. Since I believe that the Spurs will not employ an eleven-man rotation at this point in the season, it seems inevitable to me that it will come down to Finley and Mason for the role of Human Victory Cigar/Designated Shooter.