I had my ileostomy for 2.5 years. I'm a thin person, but my stomach is definitely lopsided. There is a slight slope to my abdomen as well as an indentation where the stoma was. I also have a large vertical scar which runs down the centre of my abdomen, as I had open surgeries. The lower part of the scar is keloid, but this is the part that sits below the pantline so it's no big deal. The good thing is, the lopsidedness is only visible from the top down, so when I look down at my stomach. Most people looking at me head-on would not notice the slope. The indentation where the stoma was is noticeable in certain clothing, such as when I'm wearing my gym clothes, but again you'd really have to be staring straight at it to notice. It doesn't bother me much. It's one of the things I've just accepted. I'm happy not to have the bag, so I'll take it.
The one interesting thing, though, is that I had the square outline of the ostomy barrier imprinted on my skin after takedown, and this stayed visible for quite some time. The area was definitely discoloured and even my surgeon remarked on this. The discolouration literally took 2-3 years to fade! So you may still see some changes, though you may not have the same flat or uniform stomach you may have had before surgery.