There are plenty of legends that could be brought back to work programs with people. It wouldn't hurt Shawn Michaels' legacy too much if he came back to work a program with Ziggler. There's Foley and Ambrose, obviously, and if you can convince him to actually do something good for business, Triple H is waiting in the wings so there's an opponent for Bryan. Punk can go over Austin, Miz over Rock, if Rhodes can get a clean win on Cena it would be great... And it would be the greatest thing ever if Wade Barrett went over Undertaker at Wrestlemania.
The problem is that, obviously, WWE will screw it up. See Rhodes's feud with Orton, then Booker T, which was never followed up on.