The most common and most likely answer to this crossword clue is the 5 letter word OUTRO
I've seen this crossword clue in The Times
O
U
T
R
O
Buddy explains!

The straight part
We know that "final passage" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case final passage = outro.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does OUTRO mean?
OUTRO noun- A portion of music at the end of a song; like an intro, but at the end instead of the beginning.
- The closing sequence at the end of a film, television program, video game etc.