Smith is going to struggle without Jamaal Charles, plain and simple. As soon as Charles left the game in Week 5, the Bears stepped up the blitz and ended up shutting Smith down, as he was only able to muster 181 passing yards over the course of the game. Charcandrick West and Knile Davis will likely split time out of the backfield, and while both are capable runners it won't take any special effort to stop then like it does for Charles.
Smith has the Vikings in Week 6, then gets the surprisingly solid Steelers and the ever-fierce Lions pass rushes in Week 7 and 8. All of those teams know how to put pressure on the quarterback, and will do so often.
I don't see how Smith will have the time to get the ball to Travis Kelce or Jeremy Maclin, who are the only real threats in the passing game. Even if he does manage to get the ball out, you can expect them to be smothered. I firmly believe that Smith's time as a fantasy-relevant quarterback is over.