The most common and most likely answer to this crossword clue is the 7 letter word UPROOTS
I've seen this crossword clue in Independent
U
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More clues leading to the result UPROOTS
Buddy explains!

The straight part
We know that "Completely destroys" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case completely destroys = uproots.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 UPROOTS mean?
UPROOTS verb- To root up; to tear up by the roots, or as if by the roots; to extirpate.
- (by extension) To remove from a familiar circumstance, especially suddenly and unwillingly.
- To destroy utterly; to eradicate, exterminate.