Obesity doesn't cause diabetes or insulin resistance, so losing weight won't cure it. In fact, weight gain and diabetes may be symptoms of the same cause in many people, which might explain why there are not only thin diabetics, but lots of fat non-diabetics. Why is obesity strongly correlated with Type 2 diabetes, but yet so many people who are overweight or obese do not have diabetes? What's going wrong specifically in a person who has diabetes that's not happening in just a regular fat person? I'd say that obesity is very complicated with multiple, possibly multiple overlapping, causes. What causes obesity in a person who later develops Type 2 might not be what's contributing to it in a person who never becomes diabetic.
That being said, IF you are overweight or obese at the time of your diagnosis, you may find losing weight improves, not cures, your insulin resistance. That doesn't mean you've reversed your disease, re-grown your beta cells or gotten rid of your IR. Your cells might be a little more sensitive to the insulin you make and you also need less insulin as a thinner person. If you weren't overweight, then weight loss won't be able to help you, obviously.