Question: What time of day is it when the only Day/Night card in play is destroyed, and isn't being replaced by another Day/Night card in the process?
For example, my opponent has Beneath the Burning Sun in play. I destroy it with Burrowing Beneath. There are no other Day cards in play. Is it still Day (and thus cards benefiting from the Day keyword keep their bonuses), or does it revert back to Twilight?