I've got news for you. If Manu bolts, and let's say your other scenario comes to fruition and Splitter doesn't show, the Spurs will forced into rebuilding. A Manu defection, which if he gets a crazy offer will be understandable, will devastate the franchise. That, alone, will signal a time for change, as the Spurs will clearly be stuck in that dreaded "zero zone of mediocrity."
In fact, they're already there. If they sit back, stick they're heads in the ground and pretend otherwise, then they'll be rolling with the same roster of declining, overpriced, talent they have now. Even if they can elect to slowly plug in a piece part or two gradually, as they've done, that will only prolong the sickness. If they stay mediocre for very long, they'll start feeling the pinch at the gate.
Or they can blow it up and aggressively start the process by adding young, athletic, inexpensive players, via draft and free agency, around their core of TP, TD, Hill, Blair & Hairston. Again, if you're going to lose games, it's far better to do so with young, cheap, developing talent, that plays hard and has great upside.
Either route they choose, when you factor in the changing financial landscape and limited assets they currently have, the process of remaking the roster will be a daunting one. Of course, had they elected to start the process last week at the trade deadline, they'd be a bit further along in that endeavor. However, that is another story alltogether.