I am not a health care professional yet, but I did some quick research and here is what I found: Death in patients with restrictive cardiomyopathy(RCM) often fall in one of two categories; Sudden death and chronic cardiac illness(CCI). In CCI, many patients die of congestive heart failure or similar complications. In patients who die spontaneously, the cause of death is "not very clear", but is suspected to be ischemia. For source and more info: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3390071/