It could be done, but wouldn't be 100% accurate. I could probably get it to 97% accurate, but it would take waaaay too much time. Just scan it. You can get some great gradients in illustrator obviously, but you need to take time to match the colors and angles up correctly.
Not all chars are simple shapes and fills. Check out the geese I did, and especially the Iori. They took awhile, but are filled with gradients. I find that either use all gradients, or very very few at all, and you'll get the best results.