Between those two, I'd probably opt for Charcandrick West.
Thomas is the receiving back, and West is in the carry rotation, so their different roles leave room for them both technically. Now, initially, Knile Davis was presumed to be the #2 RB, but he's been so quiet. Add to the fact that West bested Davis on the ground easily (7 carries, 31 yards compared to Davis' 2 carries for 2 yards) last week, and West figures to be, at worst, half of the rotation, with potential for much more.
Of course, if the receiving back role is purely Thomas', that sounds good for him, but he's used on so few snaps already, he doesn't just need Charles to be down, he needs a complete overhaul of himself and/or the offense.
It's possible that Reid and Smith will lean heavily on Thomas, but unlikely. It's a little more likely they'll go with West, who had better than a 4.0 YPC average last week, and likely presents the best option in place of Charles, over Davis.