Complex sentence: What will happen to them if Lady Schrapnell is never born, to say nothing of Terence not marrying Peddick's niece Maud, and thus not becoming the grandfather of an RAF pilot who bombs Berlin and goads Hitler into bombing London and Coventry ?
Split into simpler sentences: What will happen to them if Lady Schrapnell is never born? Or if Terence doesn't marry Peddick's niece, Maud, and thus doesn't become the grandfather of an RAF pilot who bombs Berlin and goads Hitler into bombing London and Coventry?