The most common and most likely answer to this crossword clue is the 9 letter word STAGNATES
S
T
A
G
N
A
T
E
S
Buddy explains!
The straight part
We know that "is left to rot" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case is left to rot = stagnates.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 STAGNATES mean?
STAGNATES verb- To cease motion, activity, or progress: