About death statistics, one thing is for certain: everyone dies eventually. Both of my grandfathers died of complications from the treatment of cancers. They were 70 and 85 years of age. One grandmother died in her sleep at home from heart failure at 91 years of age. The other is still alive in her 90's but has suffered from Alzheimers for over 15 years.
Of my parent's generation I would have to say that my parents have enjoyed the best health compared to my aunts and uncles. My mother was always conscientious about diet and exercise. Our family enjoyed a wide variety of vegetables, salads, meats, and other home cooked foods. Mom's a good cook! All in all we ate a balanced American style diet, and as children my siblings and I weren't allowed to pick and choose what we would eat off our plates. (To this day, though, I won't touch rutabaga! )
Two of my father's older brothers have died in recent years, one from cancer and the other from heart failure. One other older brother currently has cancer. My father's oldest sister recently had a tumor removed. I'm not sure about her health specifics except that she is obese.
So far as I am aware, everyone from my generation is alive and well. I know of a couple cousins who are obese, but I am not aware of any specific health disabilities.
I know of at least two children in the family who are obese. There may be more since I haven't seen some family in years. It seems to be an early warning sign of things yet to come.
So, what would happen if everyone in my genetically related family went vegan? I imagine most would lose weight. I think life expectancy would increase, especially for the men. I would hope that quality of life would improve too. Ultimately, though, people die. It may still be cancer and heart attack, but at a later age than before. Or there could be other chronic conditions that manifest themselves in the absence of heart disease, arteriosclerosis, and cancer. So, statistically that could be considered an increasing number of illnesses as causes of death, even though overall life expectancy increased.
Dave