People here underestimate Parker perhaps because of his Hollywood connection. Parker has been remarkably driven to play only for the Spurs (as long as they contend and compete and keep their nucleus which enabled them to do so), even more than Duncan & Manu, if you ask me. Duncan almost nearly fell for the Orlando lure while Manu hasn't been as coveted as the latter two (that doesn't mean that his value has been any less than Parker over the years, if not more).
Parker could possibly bolt the Spurs when Duncan, Manu *AND* Popovich leave.. but I suspect that Pop, RCB & co. are a bit more visionary than (even) we expect. If RCB pulls a rabbit out of the FA hat in 2013 (Kevin Love?) to pair up with Parker, Leonard, Splitter and the bevy of Spurs'ian role players and Pop to address a new challenge for himself as a coach... Parker will stay and the Spurs could even contend again. Heck, maybe Duncan would want to add one more season as a super experienced role player a la The Admiral in 2002/03. Besides, even if that doesn't happen and Parker seeks to leave. Would a winner like him want to play for James Dolan? No way in Gotham , I guarantee.
All said in sum, the Spurs have a lot going even in 2015 for Parker to stay put and see a team built around him, Leonard and Splitter. Not the same without Manu & Duncan.. but there is enough talent in both the NBA and among the Spurs thinktank to make alchemy work.