Sorry to hear about your friend. I think most people know to leave word of where they are going hiking with folks at home, but telling the people you are with on the hike with that you are going to be out of sight might not be so obvious.
Sorry to hear.I can see myself getting into a situation like this, hopefully not so terminal.I'm someone who values "alone time" and have to admit I'm notorious for not informing people where/when I'm going and will be back.
It's not just in case something happens to you either. In NZ we have had PLENTY of cases where people (usually tourists) have not let others know they got back OK. Search teams have gone into the mountains, risking their own lives to find people who have in fact since returned and gone to another part of the country.