The bison and prairie grass will rejuvenate the soil... it can become farmland again if need be, not that there is any shortage of plowed dirt in the Midwest.
Prairie grass and forbs make for excellent pasture - and great eye appeal, drawing in all kinds of birds. I have planted acres of prairie in restoration projects in Illinois using seed from old railroad right-of-ways. Better to see giant whitetail bucks in big and little bluestem, wild strawberries, blazing star, prairie dock, compass plant, cup plant and such than bare ground and fast food litter.
not that there is any shortage of plowed dirt in the Midwest.