The most common and most likely answer to this crossword clue is the 7 letter word SENDOFF
I've seen this crossword clue in Independent
S
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Buddy explains!

The straight part
We know that "Gathering for departure" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gathering for departure = sendoff.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 SENDOFF mean?
SENDOFF noun- A party for a person (i.e. a fellow employee) who is leaving; a farewell party.
- A party to recognize the passing (death) of a friend and allow survivors to reminisce about the person's life.