How awful for your friends!!!! I hope that they will both receive the support and compassion that they need from friends and family.
I am single, now, too. Widowed. I have the same fear as your friend...that if something were to happen to me, no one would notice for 3 or 4 days. I am scared sometimes--very scared.
I am a scientist, and I also feel the burden to be capable, strong, not need anyone--but that is my own burden, and I can lay that down, too. I've begun to admit my fear to people, too. And that's OK.
I don't know that I have any brilliant answers, here, but I do understand.