I'm sorry to read about your friend, that must have been both a shock and very sad.
There is a program in my area called "Dial a Friend". People can register for the program and then volunteers will call them once a day. There is no charge to the person being called, the volunteers are not paid and the program is sponsered by our local Red Cross in association with our area agency on aging "Seniors Resource Alliance". The Red Cross recruits and trains the volunteers, registers the people who would like to get a call, keeps the list of who needs to be called, and provides the phones and a computer to keep records. You could contact your local communtiy helpline, referral service, or area agency on aging to see if there is a similar program where you live. I'm not sure if this sort of program would have helped your friend, your description of him being fairly young and active makes it unlikely that he would have signed up. Dying unexpectantly, suddenly, does happen more often than we'd like to think about...it happens even when a person doesn't live alone. You and your friend's family have my sympathy.