Complex sentence: Sherlock Holmes and Dracula are notably absent from the League's adventures due to their assumed deaths prior to the events of the series, though the former appears in a flashback sequence, and the latter has connections to Wilhelmina Murray.
Split into simpler sentences: Sherlock Holmes and Dracula are notably absent from the League's adventures due to their assumed deaths prior to the events of the series. The former is presented in a flashback sequence, and the latter is given connections to Wilhelmina Murray.