Composer's unfinished oratorio with incomplete finale (8)

I believe the answer is:

messiaen

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'composer's' is the definition.
(Olivier Messiaen)

'unfinished oratorio with incomplete finale' is the wordplay.
'unfinished' means to remove the last letter.
'oratorio' becomes 'messiah' (Messiah is an example).
'with incomplete finale' becomes 'en' (I can't explain this - if you can you should give a lot more credence to this answer).
'messiah' with its final letter taken away is 'messia'.
'messia'+'en'='MESSIAEN'

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(Another definition for messiaen that I've seen is " French composer with centenary in two thousand and eight".)

I've seen this clue in The Independent.

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