With the Avengers movies, “the studio has breathed lucrative new life into its decades-old comic-book properties, and built a ravenous fan base for each new character it introduces at the multiplex. Now Marvel says it wants to clear the table it has spent the last 10 years arranging and make way for something new. … Audiences are about to find out what finality looks like for a motion-picture money-minting machine: Will the story actually come to a conclusion? Will characters die, and will actors leave the series?”