This is a valid question, but I guess I see it slightly different than most do. We could have locked up Murray before he had his break out year. You could see the dominoes starting to fall into place leading up to his career year. We could have extended him to a very team friendly deal at that point. We wouldn't have had to pay "career year" wages to resign him because his career year hadn't happened yet. Letting Murray go was a mistake, but probably not at the price tag he got from Philly.
With that having been said, McFadden and Dunbar actually performed pretty well, and we had hoped to get a running back in the draft. I think we entered the draft having a reasonable probability of drafting a good back, but keep in mind that we took Gregory with our second round pick. I personally believe that Gregory was deemed to be such a value at that draft slot that we deviated from the plan and took Gregory rather than a running back. It is hard to argue with that logic since Gregory was deemed to be a coup for the Cowboys at that draft position.
My biggest problem with our running game this year is:
1. We stubbornly stuck with Randle for far too long. (Doing the same thing over and over hoping for a different result).
2. We abandoned the run when it was actually working (much like we have done foe the last several years, other than last year).
3. We have failed to call running plays in critical situations, in 3rd and short to go, and ended up punting the ball (which contributed to our losing streak).
Even with all of the other mistakes we have made, we probably would have won at least two of the games we lost since Romo went down, if we had just run when the down and distance (and game situations) dictated that we run the ball, and it cost us.