The Nets don't need cap space badly enough to avoid Gasol if they're being paid to take him on. They'll have one max slot going away, and they'll need to essentially gut their team to make a second slot. With Kyrie nixing a partnership with Butler, I don't think Brooklyn feels there's any real reason to worry about cap. Marks likely won't take Mills, though.
RC_Drunkford has been suggesting trades that I think most of us feel would be very favorable to the Spurs if they were made. I don't think anyone is willing to give pure expirings for Mills, even with the Toronto pick. I also think teams would want something for taking Pau if they aren't giving back more money. But all it takes is one front office (besides PATFO) to feel like one of both of those players still has good value. Maybe such a team is out there, but if they are, they likely have their own share of awful contracts that makes taking on that extra salary tricky.