I feed a diet that is very low on pellets. Their diet is mainly hay, with some fresh cut grass, when it's available in the garden. They also have a lot of wild forage from the garden, with some green vegetables and herbs when in season. I also feed tree leaves and branches of rabbit-friendly trees.
If for some health reason I needed to stop feeding pellets, I wouldn't be too concerned, but I would make sure that I weighed the rabbits routinely once a week to make sure they weren't losing weight.