This is a pretty good theory in my opinion, but the more I think about it, it does fall a bit flat. Yes, he’s old and more susceptible to serious ailments at this point, so inhaling a lot smoke wouldn’t be good to his lungs and organs. However, I wouldn’t think it would cause a disease that would be easily curable with a simple one time remedy, such as the Night Flower. I felt like the smoke should’ve brought on a condition that was chronic, slowly getting worse overtime. Probably something to do with pulmonary or cardio issues. What I’m saying is that the smoke would cause his already fragile body to deteriorate even further, and at that point there’s little you can do to slow it down. It would be interesting to see a different scenario where, yes, he’s sick in the fourth movie, but he’ll still live on his normal life. What nobody would know however is how long he would survive for.
I do fear that his lifespan was maybe shortened, but I don’t think the LBT writers would want to show another character dying...right? Hmm...