Preserve farewell vocal work (7)
I believe the answer is:
cantata
'vocal work' is the definition.
(I've seen this before)
'preserve farewell' is the wordplay.
'preserve' becomes 'can' (canning is a kind of preserving).
'farewell' becomes 'tata' (I have seen 'A Farewell' mean 'ta-ta' so perhaps 'farewell' could also mean 'ta-ta').
'can'+'tata'='CANTATA'
(Other definitions for cantata that I've seen before include "Work for accompanied voice" , "Choral item" , "Setting of words to music" , "musical form?" , "piece of music" .)