As a hen would do when its henhouse had been demolished? (3,2,5)

I believe the answer is:

lay in ruins

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'hen would do when its henhouse had been demolished?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'as a' is the wordplay.
I cannot really understand how this works, but
'as' could be 'in' (I've seen this in other clues) and 'in' is located in the answer.
'a' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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