Here is this site that breaks it down nicely:
What Will The Spurs Salary Cap Look Like Next Year? - Pounding The Rock
So here it would be to sign, keep, and let go for this season in my humble opinion and let me know what you think.
Next Season Salary (Must be between $58 to $70 million. We can get up to $70 million before tax happens)
Duncan $12 mil (really depends if he wants to do this... 2 years at $12 million a year)
Parker $12.5 mil
Ginobili $14.1 mil
Splitter $4 mil
Leonard $1.9 mil
Neal $900 k
Jackson $10 mil
Green $3 mil (sign him for 2-3 years)
Mills $2.5 mil (sign him for 2-3 years)
Jason Thompson (Kings) Free agent signing $7 mil for 3-4 years
This would bring us to $66 million with about $2 million left over for 3 other roster spots. $1 million could be used for Blair possibly and $500k each for the other two spots.
Let go:
Joseph $1.1 mil salary next season gone
Blair $1 mil salary next season gone (depends on Duncan taking $12 mil a year)
Bonner $3.6 mil salary gone (for some type of cash or draft picks)
Diaw gone
In regards to Lebron and Wade in Miami by 2014, that could quickly change, especially if they lose tonight. If Lebron could reduce his salary to only $16 million a year to try to win a championship when he could have easily received $26 million a year, than I think Lebron in a few years would decide to go back to a small market team like the Spurs to try to win one. The Spurs will still have a nice core of talent at that time too.