I have two daughters with Type 1 diabetes. There is no cure but there is a vast amount of research being carried out into its causes and better treatment. It is vital with Type 1 that your friend is attending regular appointments with an endocrinologist at his local hospital and that he is keeping his blood sugars within the range set by his doctors. This means he needs to take control of his blood sugar/insulin levels by checking before and after every meal and injecting insulin when needed several times a day. There are two types of insulin - rapid acting (which you should take with every meal, the amount taken is determined by your blood sugar level and what you are about to eat) and a slow releasing underlying insulin (which you take once a day). The slow releasing one called tresiba continuously releases throughout a 24 hour period.
I am very concerned that you think your friend is dying and is losing weight. If he is not controlling his insulin/blood sugar levels daily - he may be in a state of high blood sugars constantly which will cause him to have a build up of ketones in his system. These are toxins and are dangerous - this can cause rapid weight loss and sometimes hair loss. He needs to see his GP asap if this is the case. Prior to my second daughters diagnosis of Type 1 - she lost weight rapidly and her hair statrted to fall out. I took her to GP and after testing her urine he sent us immediately to hospital because her ketones were very high. In intensive care they were able to reduce these back to normal levels (after three days) and started her on regular insulin. It was initially hard for her to come to terms with her diagnosis and the daily routine but - 18 months later she is living a very normal, healthy life and has been able to incorporate her new daily routine into her life. Both daughters are happy and healthy and get regular consults with GP and endocrinologist.
I would say stay clear of anyone who says they have a cure for Type 1 diabetes - all the research I have done (and I've done a lot) is absolutely clear that there is currently no cure. But there have been huge advances in recent years in ways to manage Type 1 which can allow people to live a normal and long life with the disease.
If your friend has Type 2 diabetes - that's completely different to Type 1 and it is curable with treatment and changes to lifestyle.