I don't think that player contracts/salaries would be reduced after the new CBA, whatever the salary cap numbers are.TBH, I wouldn't expect much changes there, more likely they'd shorten the guaranteed years of new contracts or something similar, but we'll see about that.
However, all of the already signed contracts would have to be honored for their length and I see no way around that unless suddenly Kim Jong-il takes over the NBA as a commissioner.All the new deals would have to be under the new regulation but there is likely to be an intermediate period, during which teams would not be punished for going over the cap due to contracts signed under the previous CBA.