Imx, players never have their PCs become turnip farmers. But, if they genuinely did make that choice then, I think, for the GM to truly be respectful of it, he'd have to make the game revolve around turnip farming - village life, bringing up kids, dealing with an outbreak of Turnip Blight. The game's high point would probably be fighting one ankheg. Forget all the end-of-the-world, cities exploding stuff, that's not what the players want.
Otoh, it may be, as pawsplay says, a refusal of the call to adventure, where the PC is at first reluctant, but we all know he's going to take up arms soon and fight the BBEG. If so, then the initial refusal isn't a very meaningful choice. It isn't telling us much about what the player wants.