The most common and most likely answer to this crossword clue is the 3 plus 5 plus 4 letter word YOU NEVER KNOW
I've seen this crossword clue in The Times
Y
O
U
N
E
V
E
R
K
N
O
W
More clues leading to the result YOU NEVER KNOW
Buddy explains!
The straight part
We know that "It might happen" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it might happen = you never know.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.