Complex sentence: Although they are able to destroy the barrier, the group "loses a year" as a price, and find that while only a few days had passed for them since they entered the barrier, for the rest of the world a year has passed.
Split into simpler sentences: Although they are able to destroy the barrier, the group "loses a year" as a price. They find that while only a few days had passed for them, for the rest of the world a year has passed.