Crossword Genius

Once finished, destroyed (12)

Ross

I believe the answer is:

exterminated

'destroyed' is the definition.
(exterminating is a kind of destroying)

'once finished' is the wordplay.
'once' becomes 'ex' (prefix meaning former or onetime).
'finished' becomes 'terminated' ('terminate' can be a synonym of 'finish').
'ex'+'terminated'='EXTERMINATED'

(Another definition for exterminated that I've seen is " Destroyed".)

I've seen this clue in The Globe and Mail.
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