So I'm about to run a one-player Vampire: Dark Ages chronicle set in Poland. I want to have the player's character abandoned after embrace, as I want to keep the cast of characters small. Is clan Gangrel my only option or do vampires of some other clans occasionally abandon a childe? Thanks.
There's certainly textual support for it:
Worse, some sires abandon their childer completely, leaving them to the mercy of the night without instruction or guidance. This fate usually amounts to a death sentence for the childe, and few last for more than a handful of nights before falling victims to their own ignorance or the torches of enraged peasants. (Dark Ages: Vampire, page 30)
The ones who tend to abandon their embraces tend to be of the Low Clans: Gangrel, Nosferatu, and Malkavian in particular. These clans don't have a lot of faith in established lineages, and might well be punished for daring to embrace at all. The Gangrel have the advantage of being able to endure the predations of nature best, what with Protean and Fortitude as their in-clans, but the Nosferatu are known for being able to survive almost any hardship and the get of Malkav… well, their sires just don't care.
And, of course, I'd be remiss if I didn't at least raise the idea that in a chronicle with one player, you're free to make any changes or exceptions you like; player characters tend to lead exceptional lives, so if your player wants a Ventrue or Tzimisce orphan, have at. But, given an interest in keeping to canon, Gangrel, Nos, or Malkavian are the ones to pick.