"Don't suppose they'll let you come with me where I'm going, Joey. I wish they could, but they can't. But I shan't ever forget you." (8.10)
Joey loses Captain Stewart and Trooper Warren in a matter of minutes, never to see them again. By this point, Joey's gotten kind of used to losing people; all he can do is keep moving forward.
"I shall die if you don't come back." (11.17)
Poor Emilie gives us a deeper glimpse into what loss feels like from the other side. Where Joey always soldiers on when his humans abandon him (either intentionally or not), Emilie collapses.
I had lost my best and dearest friend. (14.5)
Death might be the ultimate abandonment. Joey experienced this earlier with Captain Nicholls, but he wasn't as close to him as he was to Topthorn. With Albert, Emilie, and even Trooper Warren, Joey has a small shot at seeing them again. Death, however, brings the odds of reunion down to zero.