The most common and most likely answer to this crossword clue is the 2 plus 2 plus 11 letter word GO TO SMITHEREENS
I've seen this crossword clue in The Times
G
O
T
O
S
M
I
T
H
E
R
E
E
N
S
Buddy explains!
The straight part
We know that "fall apart" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fall apart = go to smithereens.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.