Complex sentence: Eventually, they must leave the valley because the Communists have other, more important people to hide, but Thanh--who is now a high-ranking Communist operative--arranges for the theater troupe to smuggle the lovers into China.
Split into simpler sentences: Eventually, they must leave the valley because the Communists have other, more important people to hide. Thanh, now a high-ranking Communist operative, arranges for the theater troupe to smuggle the lovers into China.