The most common and most likely answer to this crossword clue is the 9 letter word BREAKABLE
I've seen this crossword clue in The Guardian
B
R
E
A
K
A
B
L
E
More clues leading to the result BREAKABLE
Buddy explains!
The straight part
We know that "Not likely to last" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case not likely to last = breakable.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 BREAKABLE mean?
BREAKABLE noun- Something that is (easily) breakable.
- (usually in the plural) A set of customized hardware that is part of a drum kit. Breakables typically consist of: the drummer's cymbals including high-hats, the snare drum, the kick pedal and the drummer's stool.
- Able to break or be broken.
- Fragile.