Hello,
This came up yesterday during our Adventure 2 game.
A) What's happening to the bottom card of the blessings deck when a character fails to acquire it when attempting to close this location? Put back in the pile? Banished?
B) What's happening if I encounter the boss in another location during the very last turn, and Canyon is still open? No way to temporarily close it since there is no "bottom card of the blessings deck" anymore?
A) Vic provides the answer here, it's a normal boon encounter with the normal penalties for failing.
B) Yes, attempting to temporarily or permanently close the Canyon with no blessings in the blessings deck will lose the scenario. It's the same way trying to bury a card from an empty character deck will make the character die.
A) It's banished.
B) Hope the person at the Canyon is a Guardian and can get five charges really, really fast. Otherwise, the villain will escape there, you'll presumably end your turn (unless you can somehow move during your turn and do more explores,) and then lose.