Choir managed to hold repeated note for so long (7)
I believe the answer is:
cheerio
'so long' is the definition.
('cheerio' can be a synonym of 'so long')
'choir managed to hold repeated note' is the wordplay.
'managed' indicates an anagram.
'to hold' is an insertion indicator.
'repeated' indicates the doubling of some letters.
'note' becomes 'e' (musical note**).
'choir' with letters rearranged gives 'chrio'.
'e' doubled is 'ee'.
'chrio' enclosing 'ee' is 'CHEERIO'.
'for' acts as a link.
(Other definitions for cheerio that I've seen before include "Bye-bye" , "A final word" , "Ta-ta" , "Farewell - drinking toast" , "for so long!" .)