Lets try thinking a little strategically:
The Spurs have 2 possible objectives with such a trade. 1) Try for a championship in the remaining 2 years of Duncan & Manu. 2) Set up for the Post Duncan & Manu years.
IF 1), trading Parker needs to bring back assets that bring more basketball value, than Parker does next season. That means for example, some sort of sign and trade for a PG or a COMBO guard who brings MORE to the table than Parker. For example, CP3 or Roy (Note, I am not suggesting either of those are available, but that's the kind of TALENT we are talking). Any offseason involving Tony leaving would not fit this strategic intent unless a strong starting level PG comes in; Hill is not a starting PG on a championship team.
IF 2), trading Parker needs to bring back enough you potential to have a chance of building a championship contender around. That means a potential heir to Duncan's throne, or other potential lead dog level player. For example, Derick Favors, Greg Oden, DeMarcus Cousins (maybe).
Anything less than these two extremes means it makes far more sense to wait for the next CBA and see what happens to the value of a maximum contract; it's going to go down. The question is : how much? It may well be that TP would be sginificantly better off accepting a 5yrs/$65 million extension, which the SAS ownership might well pay. Tony has a strong incentive to resign due to the uncertainty in the new CBA...