The poor circulation caused by diabetes may make the bones softer and more likely to get fractures. If you don't have full feeling in your feet, also because the diabetes, you can continue walking on them and making them worse.
A cast might be able to get all the bones in position and keep them there while the foot heals, but not always. Surgery may be needed to put several foot bones into position and to keep them there. Often metal hardware like screws, plates, and pins are used to keep the bones in position. You will not be able to put any weight on your foot for several months while it heals.