OK, all the way back to my original question. (And BTW, thanks for all the serious and thoughtful answers.)
Today it looks like they're keeping Tyrod. If so, his guarantied money (forget about any restructuring -- the man will get paid his coin one way or another; it's only a question of how/when, bonus on a date certain or salary over time) means he's here at least two more years, possibly longer, and he's next year's starter.
That means to me it would be dumb to waste a high (first 3 rounds) draft pick on a QB this year. The Bills need instant impact/help from a lot of positions. WR? S? CB? OL? A rookie QB won't play anytime soon and while he's tying up a roster spot and his share of cap space he can't contribute anything until at least 2019.
That's what Cardale was drafted for: the long-term future. So I think keeping Tyrod clinches Cardale's future for at least three years, whether he's #3 or #2 in 2017. And I'm wondering again how they develop him, since committing to Tyrod commits to Cardale.