Parker doesn't fit with the bench unit at all. If Parker comes off the bench, he may be playing with Simmons, Anderson, Lee/Bertans, & Gasol.
That's three bad defenders, three low volume 3pt shooters, & one non shooter (Lee; not so much of an issue).
People keep saying the Spurs should let Mills walk but there isn't a viable alternative. Murray playing north of 21 mpg next season is a pretty big step and a big responsibility.
I would try and keep Mills, let Simmons walk, hope Dedmon returns (and takes the 4 year, $36 million MLE, with a player option for the 4th year), hope Manu returns and ,maybe, bring back Lee if possible.
Guards:
Parker, Murray, Mills, Green, Ginobili, 1st rounder, Forbes
Wings:
Leonard, Anderson,
Bigs:
Gasol, Aldridge, Bertans, Dedmon (?) Lee(?), Milutinov (?)