For being "75%" Lacy looked as good as he has at anytime in the last two years. If a RB is cleared to play, you play him as you would. There are always guys who are dinged up. If you adjust the roster or your game plan every time somebody isn't 100%, you would have guys coming and going every week and no consistency in the offense or defense.
Sometime the objective is to get through a game or two as best you can without upsetting the roster. They had contingency plans for getting through without Lacy. I don't think it was a bad decision at that time.