Even if he were healthy, I'm not so sure that we wouldn't be seeing Williams starting ahead of him. Jones already passed him on the depth chart and Williams is not far behind, if he hasn't already.
I had my concerns at the end of last year that Monty couldn't stay healthy at RB but also that he really wasn't all that good, except if he had a clear hole to run through. I will say, his long run against the Bears did impress me, he actually seemed to use his eyes, shift directions and find a hole that he may not have found earlier in his career.
I won't be surprised to see Monty used more as WR in the future and maybe lining him up in the backfield to keep defenses guessing. I do hope that MM has removed both him and Cobb from the playbook on third and short situations.