There is no guarantee that will kill you, but will produce a lot of suffering. Diabetes is no joke - it's expensive to treat and wrecks your body, could lead to loss of feet, legs, etc. You can't walk properly, clean yourself or maybe not even get out of bed if you are too morbidly obese. If you can walk, you will be huffing and puffing by trying to breath and likely be in pain because your feet and legs are not designed to carry a huge amount of weight. At some point, if you are so large and can't move, then another human being has to care for you while you are laying there for years waiting to die. I just don't think that would be much fun.
I'm not judging anyone who is large, btw.