I suppose, since he didn’t have time to become emotionally invested in the good doctor, leaving her to be devoured by zombies was a slightly less painful choice. And since zombies don’t usually care for gold, he can safely circle around and retrieve it once they have moved on in their never-ending quest for live flesh to eat. Heading north to Canada was a shrewd decision. Zombies hate the cold. I think. Ah, the wild west.
[Was his name a tip of the hat to Michel de Montaigne?]