When does not having a card in your library kill you?
So if I have 6 cards in my library, and my opponent has 4 cards in her library and my opponent has 7 cards in hand and I play Windfall, do I win or do we draw? Clearly she will not be able to draw a fifth card. I will not be able to draw a seventh card. Will I win because she was not able to draw a card before I was, or are we both dead?
What happens is this:
Windfall resolves. You both fulfil it's instructions as much as you can, and the game notes that you tried to draw a card and couldn't.
Windfall is done resolving now, and a player (say you) starts to get priority. As the first part of you getting priority, state based effects are checked.
The game notes that one of the states based effects is true (forced to draw more cards than were in library). It notes that it is true for both players. Because of this, both players die at the same time, due to a state based effect.
So (phew) the answer is (b) you both die.
Note: I may be slightly off on exactly what happens here - I don't know if the game state is 'noticed' during the windfalls resolution, or just after (during the SBE check). It doesn't really matter either way, but remember - State based effects are not triggered. None the less, I am 100% certain the answer above is right.