Kevin Nash is now listed as one of the names returning for the Raw Reunion show this Monday. He joins Scott Hall, Ric Flair, Shawn Michaels, and Hulk Hogan. Jimmy Hart, Billy Gunn, and Ron Simmons are also booked to appear.
This is just speculation on my part, but it would make sense for Sting to show up since The Authority is now back on Raw and Triple H vs. Sting seems to be the direction for WrestleMania 31. Also, Sting lives in Dallas which is where Raw will be this Monday.