Voit, Fedde, and Robles are the ones I could see them letting walk or try to get them to sign for less. Fedde doesn't fit into the rotation plan, especially if they can sign Anibal or some other 5th starter cheap, and is not needed in the bullpen. Robles I suspect survives until Hassell displaces him. I think for $8 million, the Nats could find a bat.
Fedde was a -0.8 WAR pitcher this year. Let him walk and sign him as AAA fodder. You can easily replace the 8.13 ERA he posted in his final 8 starts this season, after the defense improved.