"D is for Desmond thrown out of a sleigh"
There are certain and many ways, which Desmond was likely thrown out of the sleigh.
One option; he was annoying to his family there, that was a good chance a large family, as he didn't put his back in helping the family. Which ended with being thrown out by his own father, fed up with his lack of compassion, of course is blinded sighted to others if doing such an act.
Second option; goes to that he trusted strangers, to give them a ride into town, miles off ways from the snow ways. At first they seem very kind, welcoming, and very almost family or friendship areas of trust. Until, just one quick turn they stab him in the back. Fictional or not, and toss him out, leaving him out in the cold, in turns, having no choice to wander the cold winter lands, until finding help or just frozen to death.
Third option; Desmond is known in his time line, a deaf and dumb child, a teacher or something takes pity on the child, so come Christmas maybe the best gift is to stop hardship life to come, is to end his now before it, but in a place he'll feel at home and won't fight back at much. Why not, leave out in the outlands during the hazy of the snowstorm. The adult caretaker, not wanting Desmond to die, right away, but at least live how he felt pleased, before unknowingly letting winter season do its work.
Fourth and final option here, but who knows, there could be more, but for now; Desmond had an idea to make the golden angel design, compare to all his town friends could do, without his traveling merchant parents whom were speaking business, did not noticed their child, jump, but a tight curve of a thin covered frost rock, changed the angle too much, leaving for Desmond to misstep his jump, landing on head first on the rock that started it all with a healthy bone head cave-in. As the snow went on falling, covering his body forever lost in the winter wonderland.