I don't think you lose too much going from Zach to Heath Miller with Big Ben coming back, and with Charles you add some much needed depth to your RBs. You definitely win out on this deal if the guy is willing to do it. I don't see why he wouldn't just keep Charles and pick up Heath Miller though, unless he's that strong at RB.
QB- Shaun Hill
WR- Andre Johnson, Roddy White, Wes DeSean Jackson
RB- Ray Rice, Ahmad Bradshaw
W/R- Jamaal Charles
TE- Jacob Tamme
K- Rob Bironas
BENCH- Welker, Gaffney, Vincent Jackson, Reggie Bush, Sanchez, Flacco, Cooley