After classical show musical mostly returns, just having left theatre (4-9)

I believe the answer is:

post-operative

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'musical mostly returns just having left theatre' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'after classical show' is the wordplay.
I cannot quite understand how this works, but
'after' could be 'post' (prefix meaning after, eg post-war) and 'post' is present in the answer.
'show' could be 'opera' (I've seen this before) and 'opera' is found within the answer.
This explanation may well be incorrect...

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I've seen this clue in The Times.

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