It could probably also work with Collins going out instead of CP3 and the Kings sending the Spurs Len.
Looking at the return, you're effectively sending Fox and DeRozan for Castle, Isaac, Johnson, and one pick (ATL 25). That still seems like a light return. For now, the two best players in the trade are probably both coming from the Kings.
As an interesting tangent: Without worrying about salary cap stuff (which might actually work), imagine a Cam/DDR trade straight up was on the table. Do we take that? No Fox drama, none of that, just the roster we have right now does Cam for DDR make us a better team? That's a close one for me. Advanced stats lean Cam. We get bigger, but Cam doesn't push the defense needle. Cam can't create his own shot like DDR. That's kind of a big deal, because if we *do* lose Fox, DDR has maybe a bigger role on our team - if he wants to stay - than he does now. Cam can't fill that role.