George Burns smoked cigars and lived till he was 100. Many centenarians and super-centenarians have made various claim as to their lifestyle, like clean air, vegetarianism, the occasional indulgence in smoking and drinking, but never IIRC, have they made any claim that they attributed their longevity to qigong.
By the same token, many apparently healthy people die prematurely, from heart attack, cancer and other common diseases, despite living and eating well, exercising regularly etc....
So, you don't need to do qigong to help prolong longevity... but you can't say that healthy living and exercise helps either.
I'm just saying, that's the thinking behind (Taoist) qigong (breath work), whether that's true or not... draw your own conclusions.