The kind of reality we haven't experienced yet.
When in orbit, those with health problems have the option of return. On an interplanetary flight, that possibility diminishes with distance.
In case, especially, of a serious injury, but also of illness that we haven't anticipated that results from prolonged space travel, death of isolated crew members is a larger possibility.
Planning is better. It would be emotionally wrenching enough with procedures established for the crew to follow and the family on Earth to expect. Without any way to deal determined beforehand, without some ritual, reactions would be bad all around. Death, as we see, is a touchy subject, but it's equally inevitable for all of us. Preparation eases its coming.