It's not as bad as it might seem. Yes, Yeldon is a big loss. I get that. I doubt Dyer will be back, but who knows? If he is, then it's all that much better.
We still have Javon Robinson in this class. 4*. And he's a big back at 6-1 218. Could probably play at 225-230 with a 6-1 frame.
We have Tre Mason, Cory Grant, and Mike Blakely, all 4 *, and all are more speed backs, but are big enough to be durable in the 190-200 pound range.
McCaleb? NFL? Good luck son, but in reality, I think he comes back, though with the 4 listed above, could see a reduced role if any of those speedy guys really comes on strong. If Tre Mason can handle pass pro, I could easily see him taking some of OMac's playing time.
I just don't think the RB situation is going to be that bad.