The most common and most likely answer to this crossword clue is the 4 plus 2 plus 1 plus 4 letter word DEAD AS A DODO
I've seen this crossword clue in The Times
D
E
A
D
A
S
A
D
O
D
O
Buddy explains!
The straight part
We know that "Being history" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case being history = dead as a dodo.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.