Alfred Morris is the best zone running back that's on the active roster. If the line does their job, he will produce. McFadden isn't great running zone plays, but if they run man blocking schemes, he can have an impact. No one knows what Rod Smith can do when he's not running against scrubs. He looks the part, but there's a reason why he hasn't been more than a special teams demon.
Where losing Elliott hurts the most is that with him on the field, you can run the entire playbook. He excels at running in both man/zone schemes, is a good, albeit under-utilized receiver, and outstanding in blitz pickup. No other runner on the team has that package - they are all deficient in one or more areas on that list. It bears watching to see how much this impacts the flow of the offense.