Trivia: Rachel McAdams was offered the role of Andy more than once, but she wanted to do fewer "mainstream" movies. Anne Hathaway was concerned because the movie involved Andy going through a "makeover", similar to her character in the "Princess Diaries" movies. However, she accepted because she wanted to work with Meryl Streep.
Trivia: During the movie, Miranda Priestley never shouts or yells. Meryl Streep (actress) was inspired by Clint Eastwood, who can intimidate others while staying relatively quiet.
Chosen answer: Miranda was going to be replaced by Jaqueline and forced to retire. Miranda worked a deal to give Nigel's new job to Jaqueline instead. Since Jaqueline now has a job she wants, there is no one eager or qualified to replace Miranda. Miranda keeps her job. Nigel doesn't get a new job and must remain with Miranda. Miranda gets what she wants, Jaqueline gets what she wants, Nigel gets screwed, but maintains the (most likely futile) hope that Miranda will pay him back by some other means in due course.
Myridon