I would just drop Shelvin Mack for a plug and play spot on days when the schedule is weak. Having a streaming slot is more valuable than his long term prospects.
I would hold on to Sessions, Korver, Leonard and Seraphin all of them are starting to put together a decent season and most of them only have one direction to go from here, up. In a sixteen team league those guys would get scooped up in a second and you'd never see them again. All of them can make for good trade lube as well; you could use any one of them to boost a trade that improves on some of your core pieces.