As hard as it would be I cannot imagine not wanting to be there when one of my Companion Cats passed on, if just to let them know that I was there for them.
But there are people who would hate to been seen crying , and maybe thats why your friend didnt want to be there. I certainly would not like to been seen crying in public and often have to be at the Vets for a while until I regain my composure.
But I would feel badly if I was not there for my Family of Cats.