Football is a very tough and violent sport, and unfortunately injury plays a part in it every season. Coaches have one job, you coach to the players strength putting him in the best position for success. You cannot do this with fear in the equation.
The only thing that can be done to keep Dak safer is for him to make safer decisions when he's on the run. Get what you can and go down, but that being said his injury was not one that came from him fighting for extra yards.
Don't be afraid, play hard play smart and let the chips fall where they may. Go Cowboys