Ah, wondrous comeuppance. Far Cry 4 does have an FOV slider. Look, see, here's a picture of it:
See? You can slide that FOV all up about the place.
Far Cry 4 didn't have an FOV slider before it was released. It was part of a day one patch, distributed to all owners of the game. So what does it mean when some Far Cry 4 players start complaining about the lack of such an option? The game's creative director, Alex Hutchinson, summarises it succinctly:
PC players! If you're online complaining about the lack of FOV control ... You pirated the game. November 18, 2014