I see, of course, that the sudden loss of fortune is necessary for the story but in general I think it's very improbable to lose one's entire fortune so suddenly.

Granted, the vicar is a bit naive and unworldly, but would even such a man give all his money to one merchant? And this very merchant going bankrupt all of a sudden? And then, hearing it mentioned by an acquaintance without knowing about it?
All of this seems like a very odd coincidence to me but I begin to see that this kind of things will happen again in the VoW.