Stop!
This is a trade that could only happen in a video game or in trade machine. There is no reason for these deals to happen. I don't agree with your player valuations, but that isn't my main problem here. If we use your valuations this is like trading picks 8 and 25 for picks 1 and 60, nobody is giving up first pick in any draft for that regardless of salary, and nobody is giving up a top 5 player for a top 20 one.
Bingo. SA is not trading Kawhi. If you get a top 5 guy, you hold on and manage the turbulence.
You definitely trade that player if he makes it known he will not re-sign. I don't think SA can take the chance of hoping they can convince him to stay if they can acquire a pretty significant package by trading him this off-season.
Again, this is only stuff known behind closed doors, but stars get traded all the time. If Kawhi isn't happy, I doubt that is going to change much with the roster continuing to get older. Getting traded to the Cs is a whole other story and not very likely, but I have no doubt he will get traded if he isn't happy there...which is not official at this point.