Complex sentence: Waller is later attacked by Major Zod because she had taken Faora hostage, when Zod learns of what Checkmate has been doing he destroys the headquarters and seemingly kills Waller and Campbell.
Split into simpler sentences: Waller is later attacked by Major Zod because she had taken Faora hostage. When Zod learns of what Checkmate has been doing, he destroys the headquarters and presumably kills Waller and Campbell.