If you are the Spurs, I think you pay Patty Mills and to a lesser degree, David Lee and let Dedmon go. If Parker retires, I think you can get Dedmon and then you are stuck with trying to decide whether Murray is going to develop or not.
Next year the Spurs have Aldridge, Kawhii, Gasol, Parker, Betrans, Murray, Green, Kyle Anderson, Forbes, and Jean-Charles under contract - all at good contracts but Parker ($14mil) and you could argue Green ($10mil) and Aldridge ($20mil). Lee and Dedmon have player options. Lee may just accept his $1.6mil but Dedmon can get more than the $3.3 he can gaurantee on his player option. His has arguably lost value in the playoffs so far.
If Manu goes, then Patty is essential. The team loves him, he's in his prime, and his current deal has only been affordable because he blew out his shoulder in their championship season and teams backed off following his surgery (and subsequent subpar 2/3 of a season recovering).
I ma honestly not sure what happens salary cap wise if a player retires with years on their contract. For example, the Spurs are paying Duncan $5 mil this year just because. Apparently, this isn't enough money to get him in the building on game days as he has been a no show except for his retirement day.