there are several potential mechanisms by which smoking weed all the time could kill you. one of course being the smoke, since there may be a link between cannabis smoking and bullous lung disease. and then there is always the possibility of it causing a heart attack or stroke.
Marijuana's cardiovascular effects are not associated with serious health problems for most young, healthy users, although occasional myocardial infarction, stroke, and other adverse cardiovascular events are reported.
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=12412837
so anything that has the potential to trigger myocardial infarction or stroke obviously has the potential to kill you, even if it's very rare.
towards the end of my own addiction to marijuana, the way my body responded to it began to change and every time i smoked i would get an extremely elevated heart rate. 150 bpm resting heart rate while i was completely calm and sitting or laying down. if i stood up, my heart rate would shoot up well over 200 bmp and i would start to black out. this was when i realized marijuana wasn't so harmless and that if i kept on smoking it, it would probably kill me as i don't think my heart could have taken that kind of daily abuse for much longer. i was experiencing chest pains at this point as well, even as long as 24 hours after smoking. and don't even get me started on the anxiety, if i would have an anxiety attack when high my heart would beat even harder to the point where i was too frightened to even take my pulse. to this day i am left with what appears to be a permanent case of postural orthostatic hypotension from my years of marijuana abuse, although luckily the doctors say my case is mild enough to be considered benign (although it still drives me crazy to have my heart pound out of my chest whenever i stand up after sitting for a long period).
here are a couple of case reports of young men with no cardiac history who suffered myocardial infarctions after smoking marijuana:
http://www.ncbi.nlm.nih.gov/pubmed/466984?dopt=AbstractPlus
http://www.ncbi.nlm.nih.gov/pubmed/16175062?dopt=AbstractPlus
the fact that death from smoking marijuana is rarely documented by no means indicates that it is impossible. the body can have an adverse reaction to just about any substance, especially when it is abused heavily over a long period of time.