If a guest told me that they had to leave early, I would immediately ask if they had time for dessert first or if they'd like to take some with them. And if this were an older relative, I'd be doubly sure that they were served or given some. I'm not the most organized hostess in the world but I do have whatever serving implements are necessary ready, as well as containers for left-overs, so it would take only a few minutes to do so and would not take me away from the party for very long. And I am one of those from-scratch, days-of-preparation cooks. I take my hostessing responsibilities very seriously.
OTOH, if it were a request from someone of whom I am not particularly fond and who always needed special attention, I would have been somewhat put-out.