My "normal" shoe size at a normal weight would be a size 9M. Being pregnant, and then staying big for years after, my feet were a 9-1/2W or 10M. I know that I had at least a couple of pairs of leather shoes that I could not wear once I lost some weight, since they were stretched out and way too big afterward. So I would say yes, if you lose a significant amount of weight, your feet would probably get smaller, at least width-wise.
I had a weird problem recently. I
always buy New Balance shoes for exercise and I could always but a 9-1/2W right off the store shelf without trying them on and they would fit like a dream. I have probably bought at least 10 pairs like this. But just last month, I had a brand new pair which after I wore once, hurt my feet like heck. I realized the shoes were a tad too big and my feet were slipping and there was creasing in the toe area when I walked. This really bummed me out because I really love NB shoes. I took the pair back to the store and luckily they exchanged them for me for a regular 9-1/2M. I don't know if this was a freak occurence or if my feet have actually gotten less wide after losing a bit of weight