From the latest CAR, page 57:
196 Question: Imagine I have an unoccupied cloister next to an occupied shrine. I place a tile with a magic
portal which completes both buildings, and choose to use the magic portal to deploy a monk to the cloister. Does
this declare a challenge, and if so, who wins? Answer: Then it’s a challenge which ends in a draw.
199 Question: When a challenge is resolved, both the monk and heretic are removed from play. What if that
leaves one of the buildings incomplete? Can I reoccupy it using a magic portal or a follower from Carcassonne?
Answer: Gnnnn… (damn!) Yes, that’s allowed (if unforeseen).
So the answer to question 2 is yes.