I think the answer to your question would be highly individualized because we are all different and can tolerate varying amounts of fecal material in the colon before we feel sick. Some people have very regular bowel habits and if one regular bowel movement is missed for some reason, they feel nauseated, bloated, and lethargic. Conversely, others that only have a bowel movement once every couple of days can obviously tolerate increased amounts of stool and feel just fine.
No, people do not die from constipation, but they do die from things like perforated bowels caused by intense constipation. The colon can expand dramatically and accommodate a very large amount of stool. Sometimes however, the increased luminal pressure causes the bowel to rupture and liberate fecal contents into the abdominal cavity. Death comes quickly from septicemia.