Well, he's hit fine the last three years, and his career home/road splits are not drastic like you would expect from Coors (about 25 points of OPS, which is nothing). This is his first truly horrible year, and it's just a 91 AB sample. If they're going to consider releasing him, he seems to be a low risk, decent reward guy that would be worth acquiring for cheap.
Plus, if Ramirez isn't back next year, I think Stewart is a far better risk than anyone the Cubs could get on the free agent market.