Complex sentence: He is unable, however, to avert a disaster: as Svetlana rushes to the party to find Anton, she pushes Yegor and accidentally spills his blood, prompting Zavulon to break the treaty.
Split into simpler sentences: He is unable, however, to avert a disaster: as Svetlana rushes to the party to find Anton, she is confronted by Yegor. Svetlana accidentally strikes Yegor and spills a drop of his blood, prompting Zavulon to break the treaty.